Tower defense is always a popular experience on any platform, from its original iterations to popular recent additions like Defense Grid. Dungeon Defenders is an awesome addition to the genre, running on Unreal Engine 3 and playing on a multitude of devices and services including iPad, Xoom (Android), Steam, PSN, XBL, and eventually NGP. Dungeon Defenders' is a great addition to the landscape, with 300,000 active users on iOS and Android alone, and soon releasing on PSN, Steam, and Xbox Live Arcade. The game already allows cross-platform play on iOS and Android, and will add Steam (PC) and PSN to that list soon, as well as eventually the NGP, but unfortunately not Xbox live.
Dungeon Defenders is a tower defense game built completely around co-op. There are four classes, which makes sense for a game made for four player co-op. The classes are apprentice, hunter, monk, and squire, and each performs a variety of different defensive and offensive tasks. The hunter, for example, uses ranged weapons, and can lay traps instead of towers, which are high damage but only last for a few uses. The apprentice can place towers and cast simple spells, but their towers will do much less damage at once than a hunter's traps. The squire can put up shields to protect the towers, and do some solid melee damage with his sword. A good balance of classes is essentail to success, as they are designed to compliment one-another well.
The gameplay of Dungeon Defenders is easy to learn if you have ever played Diablo. While the controls are different on every verison, I focused on the PC version in my hands-ons time. Movement is handled with WASD, and the mouse is used to attack and select traps/powers using the middle mouse button to bring up a scroll menu. Some more hotkeys would have been nice, but the game is smooth and responsive and I didn't have any trouble playing. It could also be played in an over-the-shoulder 3rd person focus, but I preferred the isometric view personally.
Trendy Entertainmnet opted for an interesting micro-transaction profit model for Dungeon Defenders. While there are better items/equipment that can be bought on the store, these can be earned through simply doing well in levels. To clarify, if you complete certain challenges (like not getting hit during a level), you'll get extra money, and be able to buy the items pretty darn fast. Even with a micro-transaction system in place, due to the cooperative nature of the game, having the "top of the line" weapons and armor is not necessary to have fun and do well, and those who play well will be rewarded with them faster anyway. It's a good system that isn't intrusive and doesn't hurt enjoyment of the title.
If you're looking for a fun and enjoyable co-op strategy game, it's hard to go wrong with Dungeon Defenders. You can pick it up right now on Android, and iOS, and it will be out soon on PC, PSN, and Xbox Live arcade with cross-platform play on the first two. Unfortunatley, because Microsoft does not allow it, the Xbox Live Arcade version will not get the content updates for free either. Regardless with 300,000 players on Android and iOS already and more to comes soon, Dungeon Defenders a fun game with an active community so if you're interested in Tower Defense and co-op strategy games.