I hate JRPGS, there I've said it, I can't help the way I feel, it's mostly just the turn-based combat, but it includes randome encounters, and large overscaled outdoors map in which something(one-thing) represents an entire group of enemies. Also the 'menu-navigation' gameplay that is the combat system. All that and the androgens.
Ok, that's out of the way. I'm a Deus Ex fan, just like j-e-f-f-e-r-s. I personally feel that tight characterization and storyline is essential for a good RPG. When you've got something like Fable, for example, I felt like my character had zero personality. Sure I could customize him, but in all seriousness, he might has well have been a blank hovering monolith spreading doom and discord to the idiots who inhabited the dinky villages of the game world. KOTOR was also a good RPG in that it had characterization that allowed you to connect with the characters and perhaps invest something in them.
Alright, so I'm just waffling at this point, but I think that strong characterization, and the pacing of exposition in relation to gameplay is essential to creating that 'suspense of disbelief' that is necessary.
*On a side note, I didn't hate Mass Effect(Oh sure those bothersome vehicle sections were boring, the sci-fictioness was as wooden as Star Trek and the script read like Passions, but at least the combat mechanics were ok and it presented you with some interesting choices) but I felt it lacked depth. The issue of its originality is irrelevant when you set out to make space opera, but honestly it did feel VERY cheesily ripped off from EVERYWHERE.