I haven't been playing M&B much recently, but after looking at some mods, I'd recommend these:
WWII: China Battlefield
http://forums.taleworlds.com/index.php/board,137.0.html
Prophesy of Pendor
http://forums.taleworlds.com/index.php/board,119.0.html
Pendor is a bit more complicated than most mods, so I suggest reading the mod's forums a bit.
About the graphical improvement, I think they just replace textures and models from native, so they should work.
EDIT:
Oh yeah, forgot to mention
Native Expansion
Link:
http://forums.taleworlds.com/index.php/board,109.0.html
Here's the list of released mods:
http://forums.taleworlds.com/index.php/board,63.0.html