I'm no fan of action "RPG"s, which IMO aren't RPGs at all, having MUCH more in common with gauntlet than any self-respecting RPG, so take my commentary with that in mind.
Also, just to dump my specs here for any performance comments I may make:
AMD A64 x2 4800+, 2G DDR-400(2-2-2-7), eVGA 7600GT KO(clocked at CO speed out-of-the-box), WD 238G SATA2 16M cache Caviar
Can do Oblivious(benchmark/stability tool for me) forest scenes at 28-42fps, 36fps avg. @ 1024x768, all high details, no self shadows(still look borked/ugly to me), HDR, all extras turned on, no config tweaks, no mods. 50fps X2 4xAA. 38fps X3 2xAA. (X series benches are from the builtin/addon benches, and are the final average fps.)
In my opinion there is way too little story in Titan Quest.
Plays almost exactly like D2 without randomized dungeons, yet having better graphics, slightly more complicated/flexible skill tree/class system, and equivalent ph4t l00t. Story is entirely non-memorable, as a matter of fact from playing through the first chapter and a-half or so a few weeks back, I cannot remember much of it... Much better than DSII, so far IMO.
EDIT: Just remembered a game that might have what you are looking for: Divine Divinity. If you haven't played that gem yet then I suggest you give it a try. The graphics might look a bit dated these days (it's from 2002 and in 2D) - but it's the best hack'n'slash RPG I've ever played! Lots of combat and character development, but also a huge open world with a solid main story and lots of side quests. Again - give it a try!
For an action oriented game DD is great! Lots of quests, decent ph4t l00t(I guess), miscellaneous dialog responses that IIRC actually give different results. Graphics are meh, more like D2, but perfectly fine for me. I, surprisingly, am actually having fun with this action "RPG" although I've take a break from a few weeks back when my char hit Verdistis(sp?).
If you want more RPG AND story than action, yet still have an action bent, try NWN2. Even though the default AI is garbage(!), and the camera is crap(is/was MK's camera worse?) the game is nice. Drags at points, and the obsessive number of "cut scenes" doesn't help, yet I'ver almost finished chapter 1 and am still playing. If you zoom close in the graphics are better than NWN1, but if you keep zoom at max out(like I do) they look the same IMO. Rules are fairly close 3.5e, especially if played at hardcore or higher difficulty, unfortunately death, again, is a meaningless event unless the entire party dies. Minor technical glitches here and there as well. My numerical rating of the OC would be 7-8. The toolset is a bonus as, hopefully, we can expect some decent fan modules, and online playable persistent multiplayer worlds ala NWN1.
If you want more action, better graphics, and yet still have a story, there is G3. Granted there are a number of bugs, but they really only end up breaking a few minor quests and can in many cases be worked around if you putter around, or at least I've found that to be true of the demo. The LOD blurring of distance views is awful, but, again, can be worked around by tweaking configuration files. BEWARE: From other snarfings around the web it would appear that a semi-uber system is really needed to play on high details, but my system copes fairly smoothly at 1024x768 and high settings(haven't bothered to check actual fps yet as I haven't touched since I got NWN2), but I haven't tried 1280x1024 yet. (Saving/loading takes FOREVER for me... major blah, along with the slow panning 1st person camera. Bugs: if you've played a Piranha Bytes game before, you know the drill, if you haven't they'll patch it until it's mostly good, eventually.)
IMO
best bet for long term play value: NWN2 (user modules potential plus online worlds)
best bet for shortish term(40+h), eye candy, play once plus story: G3
best bet for uber D2 fan: TQ, Sacred Gold
best bet for D2 fan that wants a story and doesn't mind old graphics: Divine Divinity
MK: If you go by forum activity or lack thereof, MK is already dead, yet is still sold @ $50...
@txa1265:
WOW! You were GENEROUS in your MK score/review.