Woohoo! I've played a lot of it, only bits I've yet to see are the latter half of Planet Wisp act 1 (died halfway, was too lazy to try again), Silver, Egg Dragoon and Time Eater. Started playing yesterday at 2pm, played til 5:30 then got an additional hour in that evening. So a normal person should be able to see the end credits in five hours. However, I barely scratched the surface of the mission acts or red rings. I also did not replay a lot of stages, which I plan to do dozens and dozens of times just like I'd do with Unleashed (day stages) Colors and the Adventure titles.
I will say that this game is VERY replayable. Every main act is incredibly fun, and none of them make you want to play them once and never return (Unleashed did this with some of the later acts and Eggmanland).
Classic Sonic: Loads of fun, this is how Sonic 4 Episode 2 should (and probably will) control. Lots of nods to past games in later stages. Planet Wisp evokes Spring Yard Zone, Crisis City evokes Lava Reef act 2, Rooftop Run evokes Carnival Night. Power ups a fun, but not required. I did find my personal favorite set, which includes faster speeds, ring retention and shields. Overall, Classic Sonic, while simple in concept, is great fun and continues to be fun as the game goes on thanks to gimmicks and skills.
Modern Sonic: Amazing! Like Adventure meets Unleashed. I was afraid the game would be non-stop speed like Unleashed, but once I hit Sky Sanctuary I realized the game plays both ways. You run, trick and boost through areas, and slow down for 3D and 2D platforming. A lot of the stages open up to big 3D areas that remind me of the best of Adventure 1&2. Seaside Hill feels a lot like Emerald Coast in SA1, with large spaces littered with enemies and items. Overall, a great mix of what has worked since 1998, and removes what didn't work.
This is a game that I see myself playing for years, returning to it (even after beating it) again and again to find items, play with new background songs and explore different paths.
Wish I was home playing it NOW.
I might get the 3DS version for myself just to have a taste of the game on the go, despite it playing differently.
I'm not the one reviewing it for SEGAbits, but in my opinion it's an "A" release, only brought down from an "A+" because it could use more boss battles. Another three would have been welcomed. Such as sub bosses, personally I would have loved to see these three represented:
Not Rivals, not major bosses, but sub-bosses. Would have brought the boss total up to 9 to match the stage count.