The competitive mode will resemble that of MOBA-style games, or DotA Clones, whichever term you prefer. Want to hear some else that is even more awesome? Dungeon Defenders 2 will be Free to Play! I would think that they'll use League of Legend's microtransaction system for DunDef 2 so you'll get to buy hero skins and probably new heroes with access to different towers and abilities.
More information and a gameplay trailer will be shown next Friday on March 22nd.
For the game's site, check HERE