With the criteria you outlined, there is only 1 game that comes to mind. Too Human... Take a look

•Leveling up with RPG like Elements - hell yes, game has more leveling up than sp,e RPGs
•More Weapons to choose from. - check, wide variety of weapons
•Pretty Graphics. - err, cutscenes look great...
•Style-ish combo moves, like really out there Fantasy like. - Combos are great, juggle and keep afloat while in air kind of stuff
•Character Creation, this is not a must but a BIG bonus if possible. - yes and no...you choose to develop your character and turn him in to whichever style of fighter youd like
•Online Multiplayer. - yes
•Co-Op modes, Offline or Online, preferably both if possible. - yes
•DLC. - dunno
•Innovations for the Combat System, like Chaos Legion where you summon Spirit's like Pokemon. Big Plus here. - gameplay is very unique, some love it some hate it
•Storyline, doesn't need to be great but decent. - really good story
•Voice Acting, English preferably, not very good or not English > Japanse. :D - no
•And finally, RPG like-Elements in general, which games like DW6: Empires and Chaos Legion both have even though there Hack n' Slash - game is very RPGish, like diablo

Marvel Ultimate Alliance 2

Yep •Leveling up with RPG like Elements.
Deadpool's got guns and swords •More Weapons to choose from.
Yep •Pretty Graphics.
Yep, called fusions •Style-ish combo moves, like really out there Fantasy like.
Nope •Character Creation, this is not a must but a BIG bonus if possible.
Yep •Online Multiplayer.
Yep, both •Co-Op modes, Offline or Online, preferably both if possible.
The last one did on 360 •DLC.
Well, the fusions kinda •Innovations for the Combat System, like Chaos Legion where you summon Spirit's like Pokemon. Big Plus here.
Yep, right out of the comics •Storyline, doesn't need to be great but decent.
Yep, very good •Voice Acting, English preferably, not very good or not English > Japanse. :D
Yep •And finally, RPG like-Elements in general, which games like DW6: Empires and Chaos Legion both have even though there Hack n' Slash.

And you can play it on any or all of those systems (except DS but don't quote me on that).

Lord of the Rings, Return of the King -- co-op hack and slash at its finest. It's a gamecube game to play on your Wii. Level up with a just a smidgen of RPG.

Baldur's gate - ps2 or ps3 backward compatible - isometric dungeoun crawler

Marvel ultimate alliance 1 and 2 if you like the super hero thing.

PS3 Untold Legends Dark Kingdom

Xbox 360 / PS3 Conan

There are so many good ones. I loves me some hack n slash.

You might light X-Men Legends as well.

Ooohhh loving these answers so far, i have N3, looking forward to N3-2 for my 360.

As for Too Human it was okay, but it was way to flawed for many, many reasons, i still bought it for the cheap around $10 or so @ my local gamestop used, it was worth it for that price but whoever bought it new for $60 got really rip'd off.

And WTF they made a 2nd MUA? is it better then the 1st? the first one had really bad graphics...

I think you would really enjoy Dungeon Siege: Throne of Agony for PSP. It is very underrated in my opinion. It's very Diablo-like if you have ever tried that series, lots of fun.

As for Untold Legends for PS3, im glad to see you Reccomend it, though again just like with N3 and Too Human... i already have it. :/ its the best of the 3 though that much i can say. :)

It is better than the first one and I loved it.  The graphics are way better.

God of War Pwns all !
March 2010 will give you the best Hack n slash action adventure experience EVER !
Check sig for more reference.

Any  of the following would be a good choice

God of War 

God of War 2

Too Human (I didn't care for it but you might)

Heavenly Sword

Oh yeah did I mention God of War series??