Hm... if I understood you right, you might want to check these games, both 3rd person and available on PC.
Enclave - a bit old game now, but in its time it looked really good.
Viking - was originally released on Xbox, but recently was ported to PC as well. Haven't played it myself.
Oh, and I just remembered there was a (kinda) slasher MMO - Vindictus. It's not really all that massive multiplayer, though - it's basically LFD: The Game.