The matchmaking system leaves much to be desired. The fact that it always requires a full team of four to start the game is incredibly inconvenient and unnecessary. Me and my two friends can handle all but the toughest antagonists on our own, and the levels themselves can be handled with essentially the same level of ease. It would be nice if we could create a private squad, so that we could face challenges ourselves, without a fourth wheel holding us back.
Additionally, the fact that disconnected players continue to respawn and are treated as if they're still in the game is infuriating. It's bad enough that they left, but now they're also detracting from our pool of lives every time we leave an area. All in all, it seems to assume that every time someone leaves they intend to come back.