Radar Field, Lost Planet.
I spent two years with a few of my buds playing Rifle, Radar Field. Pretty much every day.
Not Lost Planet multiplayer as a whole. Literally just Rifle, Radar Field.
I've played plenty of multiplayer games, but there was something about how Lost Planet controlled; the gunplay; the specific way you shot the Rifle; and the layout of Radar Field; that ended up being magical.
Eventually you would get in a rolling match with someone and it would be intense as hell. It looked stupid, but it was insanely satisfying to roll in circles around each other for like a minute and finally get the headshot.