In terms of replayability, I think these will be great features, but I would love to see a few more gametypes put in.
Alterac Valley Style: Doing quests and controlling/destroying waypoints/spawnpoints to push towards your enemies "General".
Super Monday Night Combat Style: Push forward past "turrets" and "robots" to destroy the enemy generator. You can collect currency in the game to summon more powerful "robots" to help you complete the task as well as purchase buffs and turret repairs.
Just a few ideas I think would work great with how Diablo is setup. I don't think Capture the flag would work all that well but these are definitely styles that would fit in with the game.