DDay Normandy is a fun, addictive online multiplayer and offline singleplayer botmatch 3dshooter game. Axis vs Allied Currently there are 7 different teams you can play as, each with different weapons, skins and maps: USA, Germany, Great Britain, Russia, Poland, Japan, and Italy, and there are lots of maps for each team.
I normally don't like WWII games very much, but this is a great game. Based on Quake 2, it's engine is a bit old but it's still gppd fun. There aren't many people to play online because of this, but thankfully there are -smarter than average- bots to play offline with.