Sonic 4? Well, it'll probably be that blue-on-white logo where the robot choir sings the company name. Then, some kind of circular logo for the game, which Sonic will burst through, making an edgy hand gesture. After that, though, you'll see Splash Hill Zone Act 1 -- the entirety of which was recently captured on video and posted after the jump.
In fact, if you're not very good at Sonic, you'll see the exact series of events depicted in the video. Seriously, dude dies in, like, 12 seconds.