Ace of Spades is a free CTF multiplayer game set in a completely destructible (and constructible!) battlefield.
Huge randomly generated maps with lakes and rivers
Dig through terrain – make trenches or tunnels
Build anything – defensive positions to fortresses
Realistic gun mechanics including ironsights and recoil
Dynamic lighting system based on ambient occlusion
Up to 32 players battling simultaneously
Get it today:
http://ace-spades.com/