Sonic Generations may not be a perfect Sonic game, but it's the closest a modern Sonic game has ever gotten.
The plot is ridiculously simple; Sonic's friends gather to celebrate the heroic hedgehog's birthday, but as the party begins, a mysterious monster appears, dragging all of Sonic's friends through vortexes into various points in the hedgehog's past. Sonic sets off to rescue his friends, and along the way, meets up with his younger, podgier, cuter self, whom he teams up with. The cutscenes are few and far between, and the tale lacks character development or interesting plot points (bar maybe one late in the game). However, the story really isn't the highlight of the game and really only serves to explain why there are two blue hedgehogs running around in levels that were in previous Sonic games.
Yes, you get to play as two different versions of Sonic, as the classic hedgehog from the 16-bit era makes a return to help out his older, green-eyed self. You can switch between the two hedgehogs in the hub world, a simplistically designed area which enables you to access nine different levels from the hedgehog's past. Each of these levels are remarkably designed, looking drastically similar to the way they used to look in the games they previously appeared in, but with a different layout so the stages still feel fresh to play, as well as offering a fair level of challenge. You'll need to play through each stage twice – once with each Sonic – and both hedgehogs offer a completely different gameplay experience and different level designs.
Classic Sonic plays almost exactly as he did in his 16-bit Sonic adventures; his gameplay is entirely in a 2D perspective as he jumps and spin-dashes his way to the end of the stage. Classic Sonic's gameplay does not merely rely on speed, as there will be many points in the levels where you will be required to make tricky jumps and do some actual platforming, as well as take out many goofy-looking robot foes. It really does bring back the feel of a classic Sonic game, with the physics being much improved over that of Sonic 4 to the point where it's similar to the classic games, while only being a tiny bit clunky (though that can be gotten used to). The only noteworthy difference is that rolling downhill simply by pressing down doesn't work like it used to, but I never found this an enormous problem.
Modern Sonic, on the other hand, plays as he did in Sonic Colours; switching from 2D to 3D perspectives, the blue hedgehog can tear his way through the familiar levels at a much faster pace, while using a great variety of moves that Classic Sonic does not have. Modern Sonic swaps out the spin-dash for a boost, enabling him to move at blistering speeds, and can attack enemies by homing in on them from the air. The gameplay here is just as fun as it was in Colours, and the inclusion of platforming segments here prevents the levels with Modern Sonic becoming too easy, since you cannot simply boost to win. The controls are smooth and I found them to be much tighter than the controls were in Colours.
There are three stages per era of Sonic, with three stages from the 16-bit era, three stages from the Dreamcast era and three stages from the modern era of Sonic games, and this is a neat idea in that it celebrates every aspect of Sonic's career and chooses not to oust levels from the later stages of Sonic's career. Upon beating all three stages of an era and completing a mission from each level, you can take on the boss of that era and move on to the next. The bosses are relatively enjoyable to fight, but sadly, there aren't enough of them; there are a grand total of seven bosses, with most of them being based on previous battles in the series.
It doesn't take long to blast through the story of Sonic Generations and complete the game, but there are plenty of extra things that can be done to bulk out the experience. Each level has ten missions to complete (one of which you will generally need to complete in order to move on with the story anyway) and most of these missions are surprisingly enjoyable, with only a few duds here and there. These missions can include racing against a doppelganger hedgehog to the end of the level or helping out one of Sonic's many furry friends. Some missions even include cheeky nods to Sonic's retro days, such as keeping an end-of-level signpost up in the air until you get to the right area, or utilizing an elemental shield to platform your way to the end of a level segment.
As well as these missions, there are five Red Star Rings found in each of the main levels, and collecting them all will unlock extra bonus content such as music or concept art. These Red Star Rings can be somewhat challenging to find, though not hair-tearing difficult to get once you know where they are. On top of that, getting the best possible rank on each stage also unlocks extra content, offering yet another reason to go back to the stages to try and perfect your score (though getting the best rank in this game does seem easy, I must admit). Taking all of that into consideration, along with collecting all of the achievements, the game doesn't seem that short anymore.
Graphically the game is beautiful; the character models are sharp and look fantastic and the levels are even more pleasant to look out, with wonderful backgrounds and excellent design. The music remixes a lot of old tracks from Sonic's past, and most of them are really well-done and fun to listen to, with only one or two duds here and there. On top of that, you also have the option of choosing other music tracks from Sonic's past to listen to while playing a stage once you've unlocked them, and there are a lot to choose from. I found this to be a really neat little feature.
Sonic Generations may not be a perfect Sonic game, but, in my opinion, it's the closest a modern Sonic game has ever gotten. It offers fun levels with two different styles of gameplay, and while the story mode itself is rather short, there are plenty of missions and extra tasks to bulk out the package. If you're a fan of the blue hedgehog or of platformers, then I highly recommend picking this one up if you haven't already.