Sonic Colors discourages speed. It's quite plain and simple really.
Let's get this out of the way first, I'm not saying it's a bad game. Sonic Colors is great. I'm a sucker for the cheesy theme song, and the whole presentation and sound design is fantastic. It's also fun to play.
But the thing is, in it's level design... well, it feels slow. Sonic Colors is a lot more platform oriented. If you've ever listened to BrainScratchComms' Sonic retrospective, one of the guys hits it right on the nail - "it feels very Mario". I think even at one point Sega said that Sonic Colors was designed to appeal to Mario fans.
Sonic Colors shows this in a whole lot of ways. First off, there's the scoring system. Okay, maybe I'm just a scrub, but it is nigh on annoying to get S ranks in stages. You pretty much have to collect 80% of the rings, all of the red rings and abuse Wisp powers in a single run to S rank a stage. The game is very lenient on time limit though, so you can take your time in doing this stuff. But that's the thing - it takes focus away from speedrunning and turns it into a collectathon. You can still try to speed through a stage, but the game won't reward you for it. (for comparison, in Generations, the game doesn't give a shit about score, but the time limits are way too lenient.)
The level design is another example of this. Let's look at Starlight Carnival Act 3 - the primary focus of this stage is a yellow moving trampoline that you have to stay on. I think at some points, it feels like those auto-scrolling Mario stages...
In general though, when the game switches to 2D, the level design becomes a lot more blocky. There are general and wisp only blocks, straight angle walls and Wisps that center around precise platforming like Spike and Cube (the cube feels very similar to Mario's P-switches). And then there's the Green Wisp, which makes you a slow moving blimp, as well as the Yellow Wisp, which is abused as all hell in this game, especially in Tropical Resort.
Once again this doesn't make Sonic Colors a bad game. It's just that the level design of it doesn't feel very... Sonic. Sonic is supposed to be about goin' fast with some platforming to break up the pace.
Unleashed's problem is that it's too fast with its straight line zones. Colors' problem is that it's too slow with its Mario-like levels. Generations actually gets it right with a blend of both, not too much of one or the other.
Anyone have anything to add or contest?