Personally i never really got into the Sonic series, sure when i was young, we got the original Sonic and a console as a hand-me-down, but other than that, the rarity of new games was proportional to the special occasions we had, which only encompasses Christmas and Birthdays.
So all in all, i've probably gotten into Sonic during the 3D generation with Adventure 1 and 2's Gamecube's remakes....Heroes wasn't that good...personally i think to more newer Sonic fans, the inclusion of Team Chaotix and the random/less serious plot to the previous 2 games probably gave a bad aftertaste to the audience.....
Maybe the population of Sonic fans simply got overcome with more newer and younger fans compared to the older side of the Fanbase, so in reality, the older fans would know that the characters of Team Chaotix came from Knuckles Chaotix, whereas they'd give the idea to newer fans to recolour their own characters....and god forbid that it happened with Adventure and Adventure 2.
As a final note, i think the 2D games manages to keep a near-consistant reputation in enjoyability, though the 3D ones are usually hit or miss. (the near miss being Heroes, and the misses probably being Shadow the Hedgehog, Sonic 2006, Unleashed and possibly the Sonic Storybook games?, haven't heard much about the storybook games compared to StH, 2006 and Unleashed)