It positions itself as a marriage of all the best parts of 2D and 3D Sonic games, but still the 3D stages are only half-3D. And even that half doesn't have the complex three-dimensional level design of Sonic Adventure, so the game as a whole feels more like 75% 2D. The 3D sections are designed like tracks with obstacles, and are so easy, it's almost like the game is playing itself. Free movement is allowed, but discouraged, you can't even rotate your camera. These sections essentially serve as big set-pieces. So, even when you do execute them well, it still doesn't feel like an achievement. In fact, the 2D levels also have this problem to some extent.

But like, I just don't get the point of a 2D Sonic game in 2011. The original trilogy was great for the time, but the addition of the third dimension in Sonic Adventure created such an incredible potential, which is still yet to be fully realized. Furthermore, the constant switching between the 2D levels and the 2D sections of the "3D" levels is jarring. Because you're playing the same game, with the same graphics and mostly the same controls, but all of a sudden it lacks some of the features you were just using in a different version of this same level. I died many times trying to do a homing attack in 2D levels because of muscle memory. And you are forced to play the 2D levels to progress.

You're also forced to do these so-called "challenges". These are basically replaying the same levels, but with some annoying "feature". For example, having to stop every few seconds for Knuckles to dig treasure (and having a migraine from the sound of his radar), or having to race against an invincible version of yourself.

Playing this game made me feel like I could be playing a more coherent and/or complex Sonic game instead. This game's existence feels very unnecessary.