Sonic Unleashed can be loads of fun, once you accept the Werehog stages as Sega's Attempt at Devil May Cry gameplay.
Now, before I go on, I HIGHLY recommend renting this first. As, you may not be happy with it. The Wii version has SIGNIFICANTLY more Werehog stages then normal stages. That being said, I shall continue.
The story starts out well. Sonic and Eggman are locked in combat high up in space. As the battle rages, Sonic transforms into Super Sonic and rips through Eggman's forces. Eggman retreats to his super weapon and Sonic gives him one last chance to surrender. However, Eggman tricks Sonic and steals the powers of the Chaos Emeralds, powering his weapon, which he fires. The weapon was so powerful that is splits the planet into 7 pieces and releases a monster called Dark Gaia. Sonic is turned into a Werehog and is sent plummeting to the planet. Sonic wakes up as the sun rises and he turns back to normal. He also finds a small, amnesic animal, who Sonic names Chip. They discover that they need to fix the Emeralds by taking them to 7 shrines on each piece of planet. So, Sonic and Chip, with help from Tails and Amy, go off to fix the Emeralds, and in doing so, the entire planet.
The day stages is everything that a Sonic fan wants in a 3-D Sonic game. It's fast, quick, and seamless transitions between behind view and classic 2-D view of Sonic. Also, a new mechanic has been added to allow Sonic to perform sharp turns, allowing the speed to never decrease. Most Day time stages take a minute due to the sheer speed Sonic is running at.
The night stages is, what I like to think of, as Sega's attempt to emulate Devil May Cry. Trust me, once you come to grasp with that fact, it becomes very fun. Sonic as a Werehog has fisticuffs fighting and virtually no speed. Sonic can run on all fours to increase his speed, but it's hard to control and can potentially send you flying off the edge of the stage. There are a lot of enemies to deal with and a lot of oddly shaped level designs. Bosses require a bit more strategy then normal, simulating some of the Sonic Adventure 2 bosses. Sonic also has a sort of "Devil Trigger" ability. After increasing a gauge and activating it, Sonic will gain a power boost. The only down side is that you have to let it run out, and the boost will last longer then the battle lasts. As you complete levels, you'll get points towards upgrading Sonic, giving him new powers or increasing his stats. Overall, once you get over the fact that you are slow and have range on your attacks, the gameplay becomes much more bearably.
The sound track is fantastic. The music is done with an orchestra instead of synthed rock. Most of the sound effects are very well done, too. Voice acting is also superb, so long as you are okay with the voice change done since Sonic Heroes. When you're not running around, smashing bad guys, you are in a hub menu to travel around. From what I heard, Sonic '06 did the same thing. Overall, I'm fine with this. It's like Sonic Adventure 2's world map during free play.
I REALLY enjoyed this game, however I can see why someone wouldn't like it that much. Like I said earlier, it's something you have to try for yourself.