All-new 2D Sonic the Hedgehog in 2010

[Vixtro]

I dunno if it's because I never played the Sonic Adventure games or whatever, but I enjoy Sonic 4. I don't see what the difference is between 2D and "2.5D" because all I see is Sonic running from the left to the right on my screen, jumping on springs and collecting rings, just like old times. That's all I ask for.

2.5D means it plays like a 2D game, just the graphics are mostly, if not all, 3D.

Simple really.

[Sephiroth]

Ok I finished Sonic 4 know I have to say the game is fun if I had to com[plain and it's only nipicking here it would have to be the physics for Sonic are poor and the music is ugh makes feel sick half the time I have to mute it and I play a Sonic 1 or 2 music of that stage and that goes for Doctor Robotnik theme as well I sound like they are tacking the piss out of him with that music so I play Sonic 1 Robotnik's theme then he look more badass again.

[DeadArtist]

I'm thinking about getting this game, but it seems like all the stages are remakes of old games, so I don't know if I would enjoy this so much, but maybe you guys can help me out?
This is called Episode 1 ? How many episodes are planned ?
You can turn off the music without muting the sound, right?
Are the achievements hard to unlock?