Operation 7 is a free to play online FPS game that is aimed towards the hardcore adults. GooL mentions this game is not for the casual gamers because of the difficulty. There are many unique features in this game such as the ability to fully customize your weapon and the maps are all based on real world places!
Lately I've been playing a lot of FPS (first person shooter) games. MMORPG's seem to get repetitive at times, so I decided to play some FPS games for a while. After trying many FPS games, Operation 7 has gotten my attention. This is a great game with good graphics, many players, and a lot of customization.