#1 comes off as more of a quick snapshot then a portrait. Things like distracting backgrounds (ie chair, picture frame coming out of someone's head), elbows cut off and how the person on the left seems to have just jumped in the image make it seem rushed.
#2 Its a nice action shot, but its way over exposed. You also have alot of blur, probably due to shooting with too slow of a shutter speed.
#3 Not too bad. Comes off as a moment frozen in time, due to the chaotic action happening to the left of the QB, which is great. I would of loved to see the ball in focus and the rest blurred, but thats just me.
#4 Again, too over exposed. The subject is too centered as well
If you are shooting with a 50D and a 70-200 (2.8 or 4.0?), in sunny conditions, you should be able to get a fast enough shutter speed to freeze the action in #2.