The big problem I have with RPGs is accesibility - they need to be able to grab me and get me interested and involved at an early stage. Diablo 2 managed it, Shining Force 2 managed it, KOTOR managed it, but I can't think of many others. I (very briefly) tried NWN, Oblivion and Fable but they weren't able to 'hook' me.
In order to get casual players such as myself playing, RPGs really need something early in the game to make me feel like I'm involved, developing and eager to learn more. Don't overwhelm the player too much early on - for example, get the first level up done quickly (to give them a sense of achievement), but don't then present them with 500000 different skills/stats/upgrades etc to choose from. Keep it simple and then expand the depth of the game the more they progress. Introduce NPCs early and let them build up a long-standing relationship with the player. But also, don't forget that they player wants to see some action - if they've been running round the castle talking to NPCs, picking up quests and the odd item for 20mins+, that's maybe too long - let them get out there into some kind of really basic combat. I've seen some games overplay the storyline at the beginning of the game - yet at that point, the player hasn't really built up a strong sense of association with their character. Learning about their past is something best dealt with throughout the game, not at the start.