NWN2, definitely. Combat in both games was kinda dull, imo, but NWN2 Mask of the Betrayer oozes with creativity, while Risen is really generic. The NWN2 OC is also pretty generic, though, and if you don't know DnD very well, building a lvl 18 character to start Mask of the Betrayer can be tricky.
With mods, most games are better on the PC. Hell, even FF7 is better on the PC. This was especially true of Bethesda games. They're pretty mediocre without mods fixing lots of little things. Like leveling in Oblivion.
On normal it doesn't get that much harder, unless your a caster with low health and armor like I was my first time. Some of the bosses may pose a problem. I've forgotten where Memphis is, but I remember that I was around level 26 when I got to the 3rd act and it got hard for me around there, since they could kill me in a few hits.
On epic and legendary, however, you will die very often...
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