The fact that I'm not playing it right now.

Oh, you meant something in the game. The vehicles I suppose - I'm an excellent sniper with the tank, plus virtually unstoppable (in the tank). And the banshee is kinda fun to fly around. I was super pissed they changed the handling of ghosts for the second game, jumping them off the tank was awesome. But anyway, the game really does get old after a (fairly short) while.