Tribes: Ascend is a game that only gets better the more you play it. It's more of a thinking-man's FPS that, at first, might seem overwhelming (given the unique movement mechanics coupled with the shooting that relies more on anticipation than twitch reactions), but give it some time and the game will start delivering in spades.
Pros: It's FREE, once you get the hang of skiing, moving around becomes a joy, good music, fun gameplay (provided you invest some quality time in learning the game's ropes)
Cons: No dedicated servers, unlocks cost a ton of experience (which is earned at a snail's pace), dull art design