The ending was, pure and simply, an insult to every player that took the time to drudge to this swamp of mediocrity. If one disregards the multiplayer aspect, only the art and style remains as an interesting deviation from the ordinary.
The entire game gears up towards this mystic point where you open the vault and get 'riches, power, women' and so on. I don't think I'm spoiling anything when I'm saying that you'll end up with perhaps 200 000 extra in cash (at this point you'll be in the millions anyway) and perhaps another green or blue weapon with a shitty effect you won't care about.
For the effect that I aimed at, killing my time, the game worked perfectly. It also helped me regain my will to continue with more useful aspects of living. If at least the gameplay had changed at some point, or had required some manners of tactic thinking, or thinking at all for that matter. As someone pointed out before, all you'll ever do, and need to do, is run backwards and shoot. Strafing is pretty much optional, as long as you've got something with enough range and a scope you can pick off enemies before they reach you anyway. And if something reaches you, just pull out the one overpowered weapon you have and unload while running backwards.
I'm probably overly harsh right now, not even because I'm annoyed at the ending cause it's been a while since I've finished the game and I didn't have high expectations to start with. It's just that, looking back, I could've hired a chimp to do what I've done.