I'm currently hooked, and I mean I haven't slept about 32 hours straight on this game hooked, on GrudgeMU.
It's an odd little MMO, MU is the actual game apparently, but grudge is a custom version where it's hell of a lot different. It's all geared towards speed and progression, leveling is obscenely quick, and the combat is simplistic yet so addictive despite the grind. You can max out at Lvl 400 in about 6 hours the first time round, however you can reset to Lvl 1, 9,999,999 times, each time you reset you start more powerful than before and keep you're gear.
It sound's horribly dull but I would advise to try it, at first I wasn't sure but it's one of those games where you just can't resist to push that EXP bar a bit more, then more, then 400 levels later you reset and do it again because you absolutely must become an all destroying god with gear so shiny you will go partially blind.
Another bonus is it has a really nice art-style, all done from an almost isometric fixed camera in one corner.
Warning: contains swords the size of tree's.