This game is actually pretty popular, but unless you're in it's sort of cult or hear about it from a friend you never hear about it;
King Arthur's Gold
It's basically a game where you can be a knight, archer, or builder, then you go smash people's faces in or build people's forts in. It's ridiculously fast and for "just" the multiplayer it's free (It has a singleplayer build mode, and singleplayer deathmatch. It also has zombie mode if you pay).
This one is sort of on the same lines, but it hit steam so it's a good deal more popular;
Airmech.
You control a transformer (you can buy new ones later), and it can either be a walker on the ground or a aircraft. It also has strategy elements, as you can pick up and drop units in air mode.