I've been playing some left 4 dead lately and I enjoyed the ability to join a game already in progress. Getting into a game is almost instant this way. After the game it should move you to the lobby of the same game so you don't have to remake it again.
An option to kick players who are feeding or just suck compliments this so you can get someone else in.
so 2 things for this idea
1 - option to vote to kick a player from your team
2 - option to join game already in progress, taking control of an AI that is left after someone leaves.