Maybe it's because Command and Conquer was my first computer game, but I think that the ability to build turrets is the coolest thing to happen to the FPS genre since the invention of the alt-fire. Defence Alliance 2 supports this gift from god in the form of its Mechanic player-type. Some other mods have done it, but the way Defence Alliance 2 does it just hits the sweet spot. The Mechanic can build two different types of turrets as well as a handy-dandy ammo box which allows other players to stock back up on ammo. This helps the game to stay fresh because the other team's turrets are never in the exact same place. It also adds a dimension of team play because in order to construct a turret in any place worthwhile, the mechanic has to be covered by one or two teammates since he is unable to fire and build at the same time.
The maps play a large part in making the team work so much fun. Instead of cramping everyone into a little factory or warehouse, most of Defence Alliance 2's maps are set in little clearings outside. This empty space allows the teams to be creative. There really isn't any one spot that the defenders must be to successfully defend the map. One round you might be on a cliff defending the switch below while in the next round you might build the turrets right in front of the switch. Variety is the spice of life, and this mod is like a Cajun barbecue.
Before I started to preview this mod, I had figured that the team must be really busy because I couldn't understand what was taking them so long to release this mod. That assumption was totally wrong, the team is very dedicated and I still can't believe how much they get done in a day. There hasn't been a day since I got the preview release that aBsOlUt hasn't e-mailed me to let me know of some brand new feature that I have to go and download. The team really is hard at work, and I think you guys will be pleasantly surprised by this mod once it is finally released which should be sometime this summer.