The game was released on Steam on December 6 as an Early Access Game. The game is not fully complete yet but it is already playable with the core mechanics already up and running. That said, the developer, Trendy Entertainment is continuously working on perfecting the game while keeping lines open for player feedback.
Here are the current list of Early Access Features as indicated in the game's Steam page as of December 10, 2014:
Improved Action Tower Defense Gameplay
Every core mechanic has been refined for a more seamless experience, giving players better control over their actions. A new camera lets you quickly place defenses in the third person, and you can now move and build at the same time! Split ability and defense resources allow you to use abilities without fear of sacrificing defenses. Hotkeys let you quickly place all your defenses, use your abilities, and interact with your Defenses!
4-Player Online Co-Op
Defend by yourself or play online with up to three friends!
Special Stats & New Instanced Loot System
The game features an all-new loot system with weapons, armor and relics. Relics are powerful new artifacts that you can equip to augment your specific playstyle. Loot can now roll as either Defense or Hero focused to help you find the best items for your hero. New special stats add unique effects like stun to your cannonball towers, regenerating health, a passive heal for your blockades in a boost aura, and more! Plus, other players can no longer steal your hard-earned loot.
Elemental Combos
Now Defenses, Abilities, and Loot can combo together. For example, enemies drenched with water will receive extra damage when hit by an ability or weapon that deals lightning damage.
Environmental Traps
Unique traps are built into many environments to combo with your towers or assist in taking out The Old Ones’ hordes.
Wave Director
An all-new AI system controls the difficulty and spawning of maps. Lanes now spawn with a Physical or Magical resist tendency and are slightly randomized each wave.
New Item Enhancement System
Upgrade your armor and weapons by fusing them together!
A Whole New Enemy Lineup
New enemies add all new challenges to the game. Facing Javelin Throwers? Use Auras and Traps or upgrade your Towers early for that extra range. Witherbeasts? Take them out with your heroes before they burrow and weaken your defenses.
Plus a whole lot more
The Quick Ping system lets you help other players with hotkeys. A new bag system lets you sort and organize your inventory. The Temporary Item Box makes sure you never lose a piece of loot. Public and Private Taverns let you choose to play with the whole community or just your Steam friends! Sub-objectives let you choose to spread out your Defenses or turtle and fight more enemies.
Source: Dungeon Defenders 2 on Steam