Well, ordinarily, things like equipment management are really fun to me. I love customization, and things like Final Fantasy Tactics, where you can mix and match character skills and gear, but in Icewind Dale, I found it so clunky and difficult to manage.
The things I loved about NWN was the customization of classes in the same regard. The D&D ruleset in general lends itself well to making a character what you want it to be. Also, at that age, I found the stories of NWN and it's xpacs to be engaging, maybe not like a best seller novel, but it was enough to keep me going.
I think I prefer more of a solo adventurer kind of game when it comes to American RPGs though. I feel like something gets lost trying to manage too many characters at once, so that aspect of NWN appealed to me as well. I enjoyed concentrating on the one guy I made, so that I could make him more like something I would enjoy doing at the time, and my npc companion could just back me up, and cover my weaknesses. I also enjoyed slowly uncovering their back story, to make them seem more real, and more interesting.
I also really enjoy a lot of non-linear side quests that have rudimentary puzzles, or just interesting gear, that if you weren't checking under every stone, or talking to every person in town, you may not find it. I thought NWN did a good job of that as well. It was always interesting to be clearing out the main storyline quests, and you come across some item, and you have no idea what it does, and you finish the game and never find out what it's use was. Then, years later you come back and play the game again, and you come across someone you hadn't spoken to after getting the item last time, and you go on this whole new side quest. I guess, ultimately, that would just be called replayability, but I enjoy fleshing out the reasons why things like replayability are so important to me. Also, in that vein, character customization is a big factor to me in replayability, because one day I may feel like playing a fighter, but the next time I play the game, I may want some kind of stealthy magic-caster combination, and the ability to do that, or any other themed character that I wish makes it that much more fun to me.
Lastly, the RP elements weren't really evident in NWN, and I felt the immersion was fine. I do think however, that if a game does have RP elements, they need to be a big deal, and shape your character, as well as the path you take in the game. I think that if this game, or any other forces you to make RP choices, they shouldn't be trivial.
Hopefully this helps to clarify my position on these games, and with your experience in PoE, we can figure out if this is the game for me. Thanks again for your input.