Reposting what I said in... er, one of the Generations threads:
"I've finally decided that Generations complements Colours rather nicely. There are a few things I didn't like about Generations (and to be honest, after going back and playing a bit of Colours and then Generations, I like Colours a little more for reasons I'll get to later this week). But all-in-all, Generations is a pretty good platformer. The Classic level designs and Modern level designs work very well with their multiple pathways and platforming elements. Not to mention the fanservice with the cutscenes, attention to detail in the levels, the music, and the included levels.
"After replaying many levels for red rings, I think that the Modern levels' fun comes from trying to memorize and discover newer and faster routes in order to attain the best time and rank (plus get red rings). The levels aren't as balanced as Colours' levels, but after you try to work on perfecting the Modern Sonic levels' playthroughs, I've started to ignore the imbalance with regards to platforming and behind-the-back play (what I mean by "imbalance" is the fact that some of the behind-the-back sections felt somewhat like filler while in comparison to Colours, there was a reason for the behind-the-back play even though the majority of stages were done in 2D perspective in that title). The Classic Sonic portions, I suppose, were to complement the behind-the-back perspective of the Modern Sonic portions, but I guess what the game lacked was cohesion and fluidity in comparison to Colours. However, Modern Sonic's drifting in Generations is way better than the Colours' drifting, that's for sure.
"As I finish up the plat, I'll probably think about the game's mechanics a little more, but overall, I really enjoyed it! I thought it was a must-play. It's a very good effort on SEGA's behalf. It isn't crappy like Sonic 2006 or Shadow the Hedgehog. It's legitimately good like Colours was."
I prefer Sonic Colours, however. I know people say that in a lot of ways, due to the wisp powerups, it's less of a pure Sonic experience, but I liked the level setups, presentation (ie: audio, visuals, narrative) and 2D sections a little more than Generations. It has more of a cohesive world, nice atmosphere (including music, Eggman's PA announcements and gorgeous scenery) and a better final section than Generations did.
Generations, however, has a lot nice Modern stage design. It's extremely satisfying to find all the different paths in the behind-the-back perspective, and really fun to run those routes again and again to clock the best time. The modern mechanics work very well in this game as well. I kind of miss swimming (and maybe the double jump but I don't think it's needed here, plus it was a little awkward in Colours sometimes) a bit, though. I also can't help but to feel the final segment of the game was rushed. I didn't really like how Planet Wisp was executed in terms of the Wisps (Classic's Sonic's Spikes, in particular), and the final boss... well, I've griped about that for a while.
Thus I think they both go nicely together hand-in-hand, though I prefer Colours slightly more than Generations.
So for me, the best modern era Sonic games are:
+
+ Unleashed's Day Levels
I never really played Sonic 06, but it mostly reminded me of the Sonic OVA from 1999. City levels, kinda dark, princess character, etc.
...I... I disagree...
Sonic OVA was actually endearing. Sonic 2006 was...
Still had a blast. Yeah it wasn't "perfect" but guess is more nostalgia than anything, since compared to looking around for hidden gems, digging underground, watching long-ass cutscenes or turning into a wolf I preferred it.