Watching the game in action is totally different than actually playing it. The controls are absolutely awful. The physics are ass-backwards and there are TONS of bugs and glitches that cause cheap deaths multiple times per level.
It's quite simply an unfinished game. If this game had been given another year of development, it could have been Sonic Adventure 3.
I'm a huge Sonic fan and I am doing my best to see the good in this game, but it isn't easy. There are A LOT of problems.