YouTube: You're watching a video.
Game: You're experiencing how the game really plays like.
^ This is the difference between YouTube and the game.
Anyway, stay away the hell away from Sonic 4. Sonic Generations is the best Sonic game Sega has produced in these years, finally an awesome game, but then they revived a nightmare called "Sonic 4".
Edit: If you don't have a console that plays Sonic 4 or anything, Steam is on PC/MAC so you should be able to play its trial, if such thing exists for the PC/MAC version.
I'll be uploading the trial of Xbox 360 version to post on Digiex.