no one mentioned Sacred 2: Fallen Angels yet?

Just about matches perfectly with what Seraphic's looking for.
And it has a HUGE map.

And it's now CHEAP!

Baldur's gate Bark alliance was one of my favorite hack N slash with several of the elements you want it is a last gen game but still fun and on that like there is dark alliance two and champions of norath 1 and 2 but of those I like the first baldurs gate the best

MURAMASA!!!  Seriously, anyone would love this game but from your description it is custom made for you. 

psp - Dynasty Warriors Strikeforce, Warriors Orochi 2, Undead Knights,
DS - Ninja Gaiden
360 - Ninja Gaiden 2(if you into BC then Ninja Gaiden Black), N3, Bayonetta, Dynasty Warriors 6 and upcoming Hokuto no Ken Musou game
ps2 - just look at psp list since many of psp h'n's games have predecessors on ps2
wii - Sengoku Basara 2 and upcoming Samurai Warriors 3

that's all i know.

Ninja gaiden. When you started describing what you wanted in the game. You pretty much described ninja gaiden

Oh, and God of War 1 & 2

I played Chains for PSP but never played the original 1 and 2 of god of war.... i was to young at the time... >_>

@Spankey- i heard the CaC was crap in that game though?

Ninety Nine Nights

^Got it, good game.

Metal Slug Anthology for PSP. Very simple game but also very fun