Don't get me wrong but I think CoD has the best quit system. Yes you don't get penalized but when you quit someone else gets put in. I realize it's not very fair sometimes but to me it works.
Well, there isn't much anything you can do different with a Modern Warfare. Except situations in the campaign. Especially in a CoD game, but still give it some credit.
Hard decision, the gameplay for Reach is by far the best, but Halo 3 took MM and campaign to a new level. It was really good. Maybe not the best but still.