Do you like shooters? Do you like Real Time Strategy? Mix both two genres and youll have Tremulous.
Attending to that, when playing tremulous, you will not have to fire as if you were crazy, but you will have to manage your arsenal and take care with your movements because the result of the battle will have to do a lot with it.
Create structures to protect yourself, admin your armory, and give death to your enemies. This battle is going to be hard, but you can do it.
Choose your band, humans or aliens, the objectives are different deppending on the band you are and both two are really amazing.
In addition, it is free. What are you waiting for playing it?