There's nothing wrong with this picture. It has a good theme, the guitars and everything fit really well. And most importantly, it seems really finished.
The comical style of this piece of art is great too. The small details like the crack on the floor finish the piece completely. I also like how you did the background. Where there would normally be an ''empty'' space, is now even more detail.
Maybe some sort of audience would make it even better. Some flowers being thrown at them (Or rotten tomatoes) would give it even more an idea of a concert. Now it looks like they're not playing, especially with the drummer holding his drum sticks to his chest. Some musical notes in the piece will give a more dynamic feel.