Sonic Rush, in my opinion, seems to be the only title that truly struck the fine balance the original Genesis games accomplished.
I think what's hurt that franchise the most is that Sega seems to not really know what the hell made those games enjoyable. While Nintendo's building a Mario effin' learning course, it really feels like Sega drops a team into a room, tells them they're making sonic, and leaves a design doc that consists of a picture of the blue hedgehog and a lazily written "Make him run fast" underneath.
What's most aggravating about Sonic's modern incarnation is that the dev cycle seems to go like this.
Step 1. Make Sonic move fast. Super fast. Turn the game into "hold up and occasionally jump".
Step 2. Holy ****, our year of level construction has turned into a 45-minute game. We can't afford a one-day return cycle to Gamestop!
Step 3 (Sonic Adventure 1). Let's add a bunch of characters that move really slowly, have them go through levels that are no longer interesting because they were meant as splitzy speed-run showcases rather than, you know, challenges.
Step 4 (Every 3D Sonic and a good chunk of 2D Sonics since). Holy ****, that didn't work. Let's make all that stuff mandatory.
Sonic being fast was and still is fun. What made Sonic games on the Genesis fun wasn't Sonic blasting past everything, it was the balance of platform challenges that was strategically intermixed with short sequences of Sonic running really fast, and I think Sega's seriously lost sight of that. Probably doesn't help that Yuji Naka left.
- Sonic 4 had a really dirty "Scrappy level", and broken physics they didn't backport when episode 2 launched and fixed them. Nobody likes mine cart stages as it is, and Sega found a way to make them MORE frustrating?
- Sonic Advance didn't particularly strike my fancy, see step 4.
- I've only seen those classic Sonic levels on Youtube, where they look like a 2D version of Step 1.