Not entirely sure what you mean by "mutt hack'n'slash". Since Gauntlet and Smash Brothers have very little in common there's no context to go by other than same-screen multiplayer. If you're looking for co-op same/split screen there's quite a plethora of games to choose from these days. There was actually a renaissance for couch co-op lately (thank God)

My all-time favorite has been for some time Lord of the Rings: War in the North. Highly suggest the 360 version, but it's available for PS3 and PC as well. Though glitchy, and not the same screen on PC

Things like Halo and Gears and Borderlands are probably a shoe-in. Same with Resident Evil 5/6. Though I'd have to make a case for Resident Evil Revelations 2. That game was surprisngly good, especially surprising after how ridiculous 6 turned out to be. R2 is closer to being like a co-op 4. Still some creepiness, and on the right settings you can feel confined and afraid and at a loss for ammo and whatnot. But just like with everything 4 and after, you can become a badass by the end. Just not as much as with 6 (or 5). But it's got a gimmick with the characters that is really interesting

There's also a little known gem called Hunted: Demon's Forge that plays like a fantasy medieval Resident Evil 5 lol

If you're looking for more hacky slashy things, there's always Diablo 3 on all systems. There's been some pretty decent side scrolly ones too. Sacred Citadel is a PSN/XBLA Golden Axe style game. There's also Sacred 3 (though I'd suggest renting rather than paying full price) or one I think called FORCED?

As for Smash Brothers type games I know there's a handful of clones, rip-offs, and indie games. Not recalling any of their names though..