The structure of the game isn't too bad. The music is a bit repetitive, would be nice to maybe have a second track in there or to make this one a bit longer, it tends to get annoying.
The gameplay is acceptable, I'd give it some more options though. Instead of just running and jumping, maybe add in some ducking or weapons. Like Goku could do mini kamehameha's, Homer could throw donuts and so forth.
Which also means add in things to destroy, be it enemies or just some walls that you have to break to get through to the end. You should give the player a sense of achievement too. So not just 'run into the yellow object and play a new character.' but actually give it a sound. Show them they had a little victory and let them push 'continue with new character' or 'continue with current character'.
The basic idea for the game isn't half bad though, but the gameplay definitely needs improvement, more diversity and options for the player otherwise it will get very boring, very quickly.