I played DTV for a bit.. and it was fun for a while, but I tired of it awfully quickly. Rounds are short, and there's so, so little variation.
What I liked about DTV before was when the team would try to find a good spot from which to defend, working together to put up a shield wall, hold doorways, etc. Seemed like that required more actual teamwork than the current setup. Yes, now you need some shielders to hold the npcs off of the virgin - but there's no variation, and thus no need for tactical discussion.
The former problem with people getting 5x multiplier and then finding an inaccessible spot to camp.. couldn't you just add a 6-7 minute round timer, and if you haven't killed all the enemies when it runs out, you lose?