I basically agree with Aussie, the first things I noticed were the off-balance composition (caused by the handsome chap in blue in the bottom left), and the rather strong barrel distortion on the lines on the floor and wall.
I also noticed the shadows behind the guys at each end. I think that going for the full 90° angle with the flash would help eliminate that. That way you'd eliminate any direct flash at all (hopefully eradicating those shadows), and rely on the ceiling to diffuse it nicely.
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