The bottom right quarter of the pic looks a bit empty/scattered, as well as the lining of images in the top right.
^my attempt at critique with no basis
I like how it's done though - moreso the top right than the bottom left. The styles may be clashing a bit too much, but I don't know if that's what you were going for since it's a collage.
Like misuto said.. its kinda.. not homogenous like doesn't seem like it blends into one piece nicely. Even collages have some sort of artistic quality to it, that is to say there are good and bad collages. If flashiness and dramatic quality is what you're aiming for I would recommend to fill in the black areas more and probably use a more dynamic use of sizes of the images.
I think the top right is a good way for dynamic angles (diagonals achieve this well) The bottom left picture might have been good to have been blown up and in the background while you overlapped other pictures on top of it. You should experiment with overlapping pictures over another, masking part of the pictures and building them up :D
