It's been quite a while (about 3 months) since I've played with GIMP at all. Since the school year's about to begin again, I need to blow the dust off of 'er and work out some kinks in my memory.
I know he's not the best... BUT
I tried to bring his face out some by playing with the levels and tweaked the curves a bit, popping the colors of his garb a bit. (I always love the difference in the pic after doing so.) And I added an unsharp mask to the entire photo.
Other than that, I added a gaussian to try and help the background not distract so much, and cloned out the guy on the far right. He bugged me. Plus, I tried to put the main subject on the third.
Not perfect, but I'm pretty happy with him after being gone so long.