Tribes Ascend is a class-based multiplayer FPS heavy on skilled movement and projectile control. It's currently in beta, and new features are being added constantly. It is, and will be, free to play with a microtransaction system to unlock classes/weapons faster or to buy XP boosters.
I'm having a lot of fun with it. I won't go into detail (I'll save that for a full review post launch) but I recommend you try it out. (hooray referral links!)
I've been playing almost exclusively Juggernaut and primarily on defense, keeping my team's generator active and repairing as needed. That's partially because most teams I play on tend to just leave their generator alone, and partially because the huge blast radius of the mortar launcher is much more effective when the enemy is indoors and has a much harder time escaping it (also I'm not great at arcing projectiles over long distances).