I'll answer my own question from earlier having played Deathtrap. It's a really fun game in coop. I am playing through it with my brother. It's Diablo x Defense Grid with loot and upgradable skill trees for your character and the towers. If you liked Sanctum, Dungeon Defenders or Orcs Must Die, this is worth trying. I haven't noticed any major tech issues like their Van Helsing RPG games. The frame rate dropped when we got to like wave 20 in endless mode when there were so many enemies on the screen.
Campaign is really just a string of maps to play on. Once you finish it, there are variations on those maps which changes the layout and spawns for 13 maps x 4 tiers + random bonus levels. Still working through it, beat all but the last level on tier 2.