I think the Sonic Cycle is more of a product of its time than Sonic is. The only games that it's actually applied to are Sonic 06 and Sonic Unleashed. Everything else either turned out good (Colours, Gens, Allstars Racing), was disappointing but not unplayable (Lost World, 4) or never looked good in the first place (Black Knight, Boom). And yet it's alway posted without fail every time there's a Sonic thread. It's actually a little insulting to the people who do enjoy Sonic's recent efforts that people are using a cartoon tie-in from an outsourced developer to declare Sonic dead.
Anyway, Sonic 1 is a little dated now. The level design past Green Hill can get pretty dull and uninteresting, but I think 2 still holds up and 3K is one of the best games in the 16bit era. Honestly I prefer it to Super Mario World. I think there's absolutely room for another platformer with that kind of design as there's far more to it than just going fast. The rolling physics and momentum make for some fun speed runs and the tiered level design is really well done, so multiple playthroughs can lead to different things. I don't think declaring the Megadrive games to be bad is really very fair, because every bad Sonic game has been bad because it tried something new that didn't work or was shipped ahead of schedule. Usually, Sonic himself is fine.
I'm sort of considering going into a Mario thread, saying the series hasn't been good since Galaxy and then posting creepy fan art of Waluigi.