Sonic Advance 2 also got a lot of positive reviews, heck Sonic Rush was considered a return to the classic roots of the series, point being blue hedgehog + speed + 2D only = most reviewers going crazy over it, it's not like they realized what made Sonic so good in the first place either.
Not that I'm trying to rain on the parade, but getting good reviews for Sonic games should not be so hard, it's just so happens that they've lacked any direction and terrible QA and horrible planning and some truly atrocious game ideas, that even a okay game would be able to get great reviews so long as it stuck to what people believe is Sonic.