A test game to me and quite interesting at that.
In fact all the problems I heard about were either non-existent or very rare. I found falling to be more non-existent then in Heroes where you were almost guaranteed to fall at least once in every level. The guns weren't bad except that there was no targeting feature and the only thing repetitive were how the endings were done and the bosses.
I found the cut-scenes to be interesting, but nothing spectacular, the music wasn't half bad. The only thing I really didn't like was that the multi-player didn't have any of the other cast.
Improvements that could've been made: Adding a targeting system and allowing more freedom of the camera so you could zoom out and look down.
Most of the game complaints comes from inexperience in the Sonic world. Just slow down a little before coming to a blind spot, try to get the camera set up so that it works with the game a little better (I'll even admit, that can be more challenging than the game at times, but a little work and you can save yourself a life or two), try getting closer when using the guns since they basically auto-aim. When using the homing attack allow Shadow some hang time so you can collect yourself and go in the right direction.
This game isn't great, but it's better than having Sonic turn into another Mario and having retarded spin offs. Remember if you're having trouble, it's not the games fault, it's your fault!