>>41831044I would argue against that somewhat. Colors and Generations are as solid as 3D Sonic has ever been, and it is certainly good fun. There are still issues I have with it, but not because of "LEL NUT MAH BLACK EYED 2D SANIC."
Colors for example, while having great mix of platforming in general, it also consisted mostly of blockly platforming. This leaves out two huge features that typical Sonic level design should have: slopes and momentum building. Sure there are plently of slopes at go fast boost sections, but they're mostly scripted and not used as a level design tool other than to look flashy. The 3D sections were mostly more quick step, drift, and hallways to go fast in as a consequence.
Same sort of issues exist in Generations for Modern Sonic, but Classic Sonic sort of stands out. Ramps are scripted, spindash is way overpowered, and rolling is improperly implemented as a momentum booster. Most of the level design goes a good job regardless, but it moves away from the evolution of the level design from sequels.
As for full 2D, Sonic 4 can't into level design at all, so the off physics, non fluid character control, awful music, and base mechanics all clash with one another. Hell even fan games pull off this stuff better than either of the episodes which is why I'm sticking to them for my 2D fixes.