Your typical 3D Sonic game.
The idea of having different endings and such is indeed interesting, but in all honesty, you have to be either a little kid wanting to blow stuff up, or a hardcore Sonic fan to trully enjoy the game.
Altough the CG Cutscenes are surprisingly well done, the graphics are nothing we havent seen before either -and we're talking back to our Dreamcast times-
The inclusion of guns into the game doesnt seem to serve any purpose other than experiment a little and probably try to twist your average "Homing Attack, Spin Dash, Grind, Repeat" gameplay, and the sub-missions range from farily easy to fairly annoying, so is a good thing you can skip them.
Shadow the Hedgehog would seem like a Love it or Hate it game, but then again, you know what they say.... you're either a Sonic fan, or you're not.