Recs.
Updated
A complete reboot of the classic Unreal Tournament, with new looks, new ambitions and it's free. It has everything you'd expect out of an Unreal Tournament: shock combos, dodging, wall jumping, Facing Worlds, translocator, Fjaru doing amazing stuff on camera and so on.
Specs
Pros
Pro Lots of pro players to learn from at this early phase of the game's development
Because it's still early in this game's development (UT4), a lot of the players you'll run into are top players from previous UT's (UT99, UT2K3, UT3) and have been at the game for over 15 years. This means that yes, while you'll likely get dominated when you run into these veterans, it's also a great opportunity to better your own play. There aren't a lot of gaming communities out there where you can just jump in and immediately start playing with and learning from the best players in the world.
Cons
Con Difficult to know how big the game will ever get
The Unreal Tournament franchise has been around for over 15 years and used to reign supreme above all the other FPS's. Today however, it's much harder to predict how well it'll do compared to other top FPS games. That combined with the fact that it's a very difficult game to learn, you might end up honing your UT skills for nothing at the end of the day.
Con There's a huge skill gap
Many of the players currently involved in the community at the moment have been playing Unreal Tournament for over 15 years. If you're new to the UT franchise or arena shooters in general, there's a chance every time you boot up the game that you'll run into and get trucked by those vets.
Con Constantly changing game mechanics and balancing
Because the game is still in "Pre-Alpha," the game has the potential to change in both major and minor ways from build to build. The majority of your gained experience will transfer from build to build, however it can be a bit of an annoyance having to relearn balances over and over again.