I'm kinda split on this game, I really enjoyed all of the 2D levels, but I still don't like 3D Sonic gameplay. The FOV always makes it so your character is minuscule in the screen so it's hard to do precise movements, and the homing attacks are the furthest thing away from skill based gameplay.
However, the 2D stages are so good that I don't care, the platforming is tight, the levels are beautiful and the music is just phenomenal. That being said, it's all far too easy and the physics are a bit off to be mistaken for actual classic Sonic.
Anyways, for me, Sonic Generations is worth it for that alone, if you like 3D Sonic too then this is a must play.