Way too much hate for this game. I think people punish this game because of the hype it did not live up to. It has problems, but I rented it from Redbox last night and had a lot of fun.
For $20, I think you could play it for 10-15 hours, get your fill of fun and achievements, and then resell it. That would be my recommendation. I can't wait to go home and play it, but I feel everyone's frustration with AI funny business, certain objectives being near enemy spawns, and shooting mechanics.
If they tightened up the shooting controls and fixed multiplayer lag, I would have a blast with this game.
I am jokingly exaggerating, but Brink is horrible. I'm sure you probably could get it for free soon, because there will be mountains of this game in landfills. I spent 12$ on it, and still felt like I was majorly ripped off.