What are the best hack n slash / beat em up games?

I second SACRED CITADEL, a often overlooked title that ive enjoyed more then Shank (wich is awesome as well).

I also add KUNG-FU STRIKE- each level is a tight arena rather then the 'walking arenas along a level' kind of beat n ups but is amazing, with refreshing controls that feel much better then any other title ive played, the way counters and such not only work well and feel right, the whole set of moves are needed and useful and you feel like a kung-fu master.

DUST an Elysian Tail is great, and goes a different way; theres less button mashing oldschool, but few combos used creatively- and its freaking awesome!

And... MARLOW BRIGGS if you're looking for a god of war clone with character and lots of humor; Short but i enjoyed it much more then any DMC, more then Darksiders and i was laughing and smiling all the way trought- something few games did.

Extra:
VOLGARR isn't quite beat n' up, as it is more oldschool platformer then beat n' up but the fighting past the first level (you will take some time on the first level) feels a lot like those between slashing(+crouched and air), dodging, downard-drop attacks and trowing spears[thats the entire move set right here].
Its not like most beat n ups with lots of mindless button mashing and tons of combos with little difference (like more damage or area here and there)- its more like dark souls on platforms, with amazing tight controls where once you get in each move is tought and well applied.
But its HARD, HARDCORE, the non-cheap and extremely rewarding kind. No fake difficult, no hand holding. It will feel overwhelming at first and the first time you encounter certain obstacles will seen sadistic- until you understand it both rationally and unconsciously on a dextery/coordination level; Its mastery, patience and FUCK YEAH I OWNED YOU ALL LIKE A TRULLY VIKING like no other title. And manly as hell.
'RISE WARRIOR'
-Odin, Volgarr the viking

Torchlight 2, Diablo 2, Path of Exile and I think that Borderlands is a beat em up game

i really like the 99 nights over xbox(hope it got a steam version someday),another good one is dust but if you want a diablo experience go for path of exile, damm good and hard game since you got only 1 life on hardcore mode.