Sonic Generations is a good homage to Sonic over the generations with a lot of well picked levels and fun gameplay
Generations certainly has a lot of flaws though, and while playing through it I made sure to tell the game what it was doing wrong, although that may just be me yelling at it. For one, playing as Classic Sonic just has some weird physics to it. You just can't jump pass a certain height, nor do you carry much momentum when jumping, and curling into a ball while running actually slows you down opposed to speeding you up like it used to. On top of that, Classic Sonic gets a very heavy knockback whenever he gets hit by enemies, which can be quite annoying when you get hit again when you are recovering from just getting hit.
Modern Sonic has some odd physics too, but it just takes some getting used to. Like his homing attack will pretty much cancel any momentum you had and drop you straight down after it's done with the attack. His other main feature, boosting, can help you get further than a homing attack, but its far harder to control and more often than not just send you dying if you use it wildly. Boosting is still pretty great as it still uses the unleashed physics, but it can get really troublesome when the stages switch from a 3D to a 2D layout. And that's the main problem with Modern Sonic's stages, unleashes physics just don't work well with a 2D design as it was built for a lot of room and the ability to see where you are going. So when you are boosting as Modern Sonic this can often lead to some untimely deaths that where just not able to be seen. But 2D only happens a few times throughout levels and really isn't noticeable till the last few stages.
The story in Generations also failed to meet my expectations. What could have been a grand adventure through time and space just felt like "hey, guys remember this level? Pretty awesome right?" For the most part, none of the stages were original, and often left me wanting something a little new and fresh. Perhaps, I would have like this game a lot more if at the least the story gave some kind of connection to each stage with like a cutscene or something. I mean, we are traveling through time and space right? I'd like to hear a better explanation then, let's just randomly go to some of the best levels in the Sonic universe! Perhaps, I'm being too harsh on this game, but the story really left room for desire. Sure there are a few inside jokes, and a somewhat decent amount of cutscenes, but I just felt that they lost a lot of potential storytelling, something Sonic Adventure 2 excelled at.
Still, Generations is a blast to play through, and it nowhere near has as much problems as the Sonic Adventure series, or Sonic Unleashed did. All the stages that come back are well picked, and are iconic to the games they are from, but unfortunately there are no space levels, despite being the usual last zone. The challenges the stages have are also some of the best challenges the Sonic series has ever had; with many of them being varied and never getting dull. One challenge in particular, the Episo grappling hook one, is something I want to see more of. Generations also has a well thought out design for online ranking called 30 second trials. I was very impressed with the idea of getting as far as you could in 30 seconds, and I would certainly like to see more in upcoming sonic games. Most of the bosses were also very fun to play against, and wanted me to play more bosses like them, especially the rival boss battles. The only boss battle I hated was the last one, because in the end it was just mindless boosting. But by far the best thing about Sonic Generations: all the new organized music. Just a lot of the remixes and remakes of the songs of past Sonic games make generations soundtrack stand out so much, and the fact you can play them on any stage once unlocked? Wonderful.
Conclusion: Sure, the Story is subpar and the physics require some getting use to, but Sonic Generations simply offers too much of the good than the bad. All the returning stages were well picked, and seeing them in new 2D and 3D renditions is a blast. The challenges for each stage are also the best any Sonic game has ever offered. The remixes of past Sonic music are also well done and are clearly a love letter to the fanbase. Overall, if you ever wanted a brief history on Sonic, Generations would be your first stop.