Some problems and frustrations keep Sonic Unleashed from being what it could've been, but it's certainly not a bad game.
First thing to discuss is the plot. The game opens up to a cutscene showing a large air fleet in space, created by none other than Dr. Eggman himself. That's when Sonic jumps onto one of the ships, an explosion behind him. After some action of Sonic running around and smashing Eggman's play-things, Sonic confronts Eggman in his giant mech. Eggman grabs Sonic to no avail, as he goes Super Sonic using the 7 chaos emeralds. Busting up Eggman's mech and his fleet, he chases Eggman onto one last ship. This leads Sonic to being caught in the evil mastermind's trap, which sucks all the power from Sonic and the chaos emeralds. Not only that, the ship is actually a giant laser that shoots the Earth, breaking it into pieces and unleashing Dark Gaia, an evil creature who sleeps within the core of the Earth. Sonic is affected by Dark Gaia being released, and turns him into the Werehog, a wolf-hedgehog hybrid thing (it also is an incorrect name: "wer" means "man", calling Sonic a "man-hog" technically). Eggman proceeds to dispose of the man-hog and launches him at Earth, while Dark Gaia, who is not complete due to the rude awakening of the evil doctor, spreads across the globe in little, purple glowing things.
After being launched from space, Sonic crashes into Earth unharmed (looks like being the man-hog made him invincible). He looks around and notices a little fairy-pixie thing unconscious, to which he wakes up by being shaken violently (because shaking violently is always the answer). Scared of Sonic's monstrous appearance, he takes cover behind a rock. Sonic asks him if he's OK, to which he says he's fine, followed by calling Sonic "Mr. Monster Guy". This makes Sonic realize he is a werehog now (surprised he didn't notice that before). He doesn't know what has happened, and decides to ask the fairy thing his name. But of course, he doesn't know, because he has amnesia for some odd reason. Sonic decides to help him recover his memory, when the sun rises. That's when Sonic goes from evil beast to normal self. The fairy guy is amazed by what happened.
Sonic and the fairy soon arrive in a city called Apotos, where Sonic (juggling 7 energy-drained chaos emeralds in his hand) tells the fairy what happened. But before long, the fairy sees an ice-cream stand (where we learn he has a sweet tooth) and, of course, buys an ice cream cone from the ice-cream man (who looks and sounds eerily similar to Morshu of the Zelda CD-i games). Sonic and the fairy begin to continue walking and Sonic decides they should look around to see if the people recognize you. This is where he names the fairy "Chip" after the ice-cream, saying he needs to be called something until they find out who he really is.
It isn't long before Sonic and Chip run into Tails, who is being attacked by evil creatures of Dark Gaia (although, he could just fly away and be safe). Sonic (who is in Werehog form) beats them all up and saves Tails (who, again, could fly away), who is shocked by Sonic's new appearance. Sonic tells Tails a story, and Chip pulls a chocolate bar out of nowhere. Tails tells Sonic to go visit a man named Professor Pickle in Spagonia. Tails proposes using his Tornado-1 (whatever happened to 2?) to get across the continents quickly.
Sonic and co. soon find out the professor was captured by -- guess who? -- Eggman. Now the crew has to go the Mazuri and save the professor. So once in Mazuri, Sonic and friends find Professor Pickle stuck in a glass cage thing, where he is complaining about sandwiches. Tails gets him out, and Sonic (he's a werehog at the moment) breaks into a vault to recover Gaia manuscripts Eggman wanted the professor for. So they get out, but when they get back to the village (which is now daytime all of a sudden) and see Eggman is there trying to get something from the villagers, who proceed to throw rocks at the fat man. Enter Sonic, who destroys the robots of Eggman and proceeds to chase Eggman and soon confronts him in the Egg Beetle. He destroys the robot and then finds a Gaia Temple, which Eggman was looking for. The temples are the key to fixing the planet. By placing a chaos emerald on a pedestal, the chaos emerald regains energy and puts a piece of the Earth back into place. The story goes on from here, with Sonic going to temples and putting the Earth back together (I'm pretty sure some crazy glue would work just fine though). In short, the story is sub-par, involving Eggman once again bringing an evil creature back to life (because we all know that worked out so well the previous times).
While traveling from stage-to-stage, you get to explore the hub worlds of the game. Hub worlds have two separate sections: the main city where you meet towns folk and talk to people (exciting!) and the Gaia Gates, where you access stages and can find hidden goodies. Within the town, you converse with people to learn pointless information about lives and access some missions. Other than that, they're mostly filler (although beating up pedestrians can be fun, and there are a few medals to be found). Gaia Gates are different than cities, and for the better. The gates offer more purpose, as they are your gateway to the stages of the game. As previously stated, you can also find goodies like music tracks, images and art, and medals.
If you want to go into stages, you will need to find medals. There are 2 types of medals: Sun and Moon. Sun Medals are necessary to access the Day Stages, while Moon Medals are for Night. Medals are hidden throughout stages and in the hub areas. Each level needs a certain "level" of medals before you can enter. The medal level increases when you get a certain amount of medals, and Sun and Moon Medals have their own levels. Moon Medals are more common in Day Stages, and Sun are more common in Night. These medals are tricky to find, and necessary for game progression. This is a downside, as this may involve back-tracking and visiting previous levels just to move on, which can get tedious and annoying.
Different hubs/cities are accessed when you complete certain levels and speak with Professor Pickle. His laboratory in Spagonia is where you have to go whenever you need to speak with him. You have to visit him multiple times, which is repetitive and boring. You can also give him souvenirs that can be bought at stands within the hubs. You can also buy food items to increase your experience points.
There are two types of stages: Day stages (with Sonic) and Night stages (with Werehog). The Day stages use both 3D and 2.5D gameplay within stages. The Day stages are usually focused on fast-paced action, which the main goal of these levels are to get to the Goal ring at the end of the stage. The stages are often considered the high-point of the game, which is true. The game features satisfying fast-paced action and good platforming. Sadly, the Day stages has it's share of problems. First off are the controls: you'll be going so fast, Sonic won't be easy to control, and you could easily run into enemies or fall into a pit. The stages also occasionally feature poor level design and will often make you use trial-and-error. Even with these, the Day stages still have more pros than cons, and are just plain fun to speed through.
Collecting rings in Day stages fill up Sonic's boost meter, which gives Sonic a burst of speed that can destroy obstacles, defeat enemies, and make Sonic go stupidly fast. While Sonic is in the air, you can perform a homing attack to attack enemies and can chain homing attacks when multiple enemies are around. This trick is useful for crossing gaps and quickly disposing of enemies. The jump and homing attack are set to different buttons, so for those in the habit of pressing jump twice to perform the move, this could take some getting use to, but you should pick up on it easily. As you progress through the game, Sonic learns new skills like light-speed dashes and wall jumping.
The Night stages feature Sonic's Werehog transformation. This portion of the game focuses on combat as well as platforming and some puzzles. At points in a stage, enemies will appear and you must defeat them to progress. Enemies vary from flying enemies who slam into you to the common foot-soldier enemies. Most of the enemies you'll encounter are the spawns of Dark Gaia, although you'll occasionally encounter Eggman's robots running around. Combat involves the use of Sonic's stretchy Werehog arms to fight (what is this I don't even...).
Defeating enemies releases experience and Gaia energy, which fills Sonic's "Unleashed" gauge, which when activated, makes Sonic glow blue and become more powerful and increases the speed of his attacks. You'll be running into a lot of combat, so if you aren't a fan of the fighting, than these stages will tend to drag on (although this could be because of how long the night stages are: most are 20 minutes or more). If you do enjoy the fighting, you'll have plenty of satisfaction killing things. When fighting enemies, knocking their health down to a certain point allows you to perform Critical Attacks, which are quick-time events to finish off your enemy with style. These also give you bonus points and extra experience. Werehog Sonic can also block attacks, which is useful when being attacks by multiple enemies. You get a certain amount of shields, and can collect more throughout the level if they break.
Night stages also feature platforming segments and even puzzle elements. The stretchable arms of the Werehog (I still don't even...) are largely used for these areas. Along with the jumping on and across platforms, you can grab onto ledges, swing on and latch onto poles and certain objects, and do other tasks. You may also have to push boxes and objects and carry small objects to access parts of the stage. With controls that work, the platforming is fun to play, even if you won't see it as often as combat.
The game features a level-up system where you can increase your stats by collecting experience in Day and Night stages. Defeating enemies give you experience. At the end of the stage, you are able to use the current amount of experience you have and upgrade stats, although you can do so in the middle of stage by selecting "Status" from the menu. Sonic uses two stats, "Speed" and "Ring Energy", while Werehog has "Combat" (to teach him new moves), "Strength", "Life", "Unleash", and "Shield". You'll typically find more experience in Night stages, where the enemies are more numerous.
At the end of each stage, you are given a ranking on a scale of S to (S is the best, E is the worst). These are mainly based on time, number of rings, and points from defeating enemies and doing other tasks. When you die and respawn at the last checkpoint, your current points are reset to 0. This makes it necessary not to die if you want the best rank you can possibly get. With poor level design in Day stages and the length of Night stages, dying may happen a couple times. This leads to frustration, as you would have lost all the hard-earned points you had earned. Perfectionists especially will feel like they want to throw their controller at the wall. Thankfully, the game is pretty lenient with giving ranks, so if you aren't too far in a stage and die or can get enough points from your last death, there is still a chance for a good ranking. Between trying to get that S rank and collecting every collectable within the stages, there is a mass amount of replay value in the game, so you'll be sucked into the game for hours on end.
What's really nice about the game are it's visuals. The game uses an engine called the Hedgehog Engine, which is a graphics engine used to make CGI-quality graphics in-game and uses light-reflection to create a realistic look of stages and Sonic. These graphics do look very great, and are a nice touch. The framerate, on the other hand, sometimes slows down, more noticeably in some cutscenes, which is a bit of a graphical issue. The music is great, not focusing heavily on the rock formula previous Sonic games have used many times. The sound effects are good, and surprisingly Sonic's voice isn't that annoying in this game. Sadly, the same can't be said for... just about everyone else. Chip doesn't shut up, Tails is annoying and unbearable, and Professor Pickle is just unlikable.
PROS:
*Great opening cutscene
*Fast-paced and highly enjoyable Day stages
*Night stages aren't bad either
*Lots of combat, if you like the combat
*Platforming and puzzle segments of Night stages are done well
*Tons of replay
*Impressive visuals
*Good soundtrack
CONS:
*Lame story
*Hub worlds are filler, and the townsfolk are useless
*Back-tracking to find medals is annoying
*Constant trips to the Professor
*Poor level design and control quirks in Day stages
*Lots of combat, if you don't like the combat
*Long night stages
*Frustration is imminent
*Annoying characters
Score Breakdown:
*Presentation: Decent
*Gameplay: 7.5
*Replay: 9
*Graphics: 8.5
*Sound: 8
*Story: 4
Final Score: 7/10
While I think Sonic Unleashed is certainly a good game and it has a positive score, I would recommend you rent it. Most people can find enjoyment in the high-speed day stages, but there will be those who will not be content with the night stages. But any fan of Sonic should have this game, or at least give it a try. You may be pleasantly surprised.