Excerpt: I was addicted to the original Natural Selection, and it kept me hooked for many years - it was a free add-on (known as a "mod") for the Half-Life game. Now it's back - similar in some ways, different in others - bigger, badder, and even better ! The game now uses a bespoke 3D engine called Spark written by the team themselves, because nothing else available seemed to be advanced enough to do what they wanted.
Pros: Cheap, fast exciting gameplay, never the same game twice, mods give you more "free" games
Cons: Official maps thin on the ground, steep learning curve for commanders, reasonable PC required