Pedro The Hutt said:
I'd say there've been several decent to good Sonic games after the Sonic Adventure days. It's just that Sonic suffers from a fanbase that is impossible to please. Even on the occasion that Sonic Team makes exactly what the fans have been asking for (Sonic 4).
Indeed Pedro! There have been several decent to good Sonic titles after Adventure. Technically, Heroes was mediocre and the rest were well... "forgettable" or plain "terrible". Sonic 2006 was truly terrible because of its botched execution due to lack of development time. I can see what Sonic Team wanted in theory for this game but, they rushed it out - leading it to become the abomination that we know today. Sonic Unleashed was (very) good if not decent - though as we probably know, the Werehog (actually ïlwolf would be the proper term but, rule of cool) was one of the major weak-points. Then again, the werewolf wasn't that bad, just quite repetitive. If they had more time for development, they could have "spruced" up the concept a bit more. Sonic the Hedgehog 4 was also decent but, the game was a bit too easy (episode 1 final boss notwithstanding) and the physics being too floaty. Colors was truly the game where they perfected it (though I kinda missed the hedgehog, and a level on par the difficulty of Eggmanland).
But yeah, the fanbase of Sonic is one of the worst I have EVER seen. Long story short, it almost seems like they refuse to be pleased. Sonic Team has no hope for appeasing them. I really hope they take the path of Modern Sonic (with sporadic classic-like outings). Personally, I loved all the Genesis titles, the Adventure series, Unleashed, and Colors and am looking VERY forward to Sonic Generations.
tl;dr: Not all post-Adventure Sonic games suck - just aren't exactly on par, I loved quite a few of them, the Sonic fanbase is one of the worst, and I am looking forward to Sonic Generations.