Sapphire Tears
You can see a youtube video of it in action
here.
The game is pretty simple, it doesn't have super great graphics, but it has a somewhat unique feature.
Before you start a match, everyone can build blocks on the map for a small amount of time to make their own base, sniper tower, or what have you. This also makes very interesting gameplay during the Capture the Core (pretty much CTF) game mode, as you can try and hide it in your base using pretty odd methods.
You also end up picking two weapons (shotgun, sniper rifle, etc), and two abilities (scope, stealth, etc) before hand, but you can only change the abilities in game, and only when you end up dieing.
The only problem with this game is how unpopular it is, and it kind of hard to find people online in it, so if you want to play you should probably first try and get some friends.