Skulltag
It's a multi player doom, and where I learned how to play
FPS.
I'm not sure if the original WAD is required or not, as my friend installed it for me, but it is really fun and really fast paced.
Death match is like a battle between a buncha' scouts with every weapon and speed hacks
I like the survival modes, where you play through games without dieing, and if all the people playing die, you start the map over.
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The Man, The Legend, The Verge

Jumpin' on the ol' band wagon!