The hardest problem I have with replaying games is that while I love the idea of having a new experience, I tend to form emotional attachments to the NPC's in my party (assuming it's a party based game). I'm replaying BG2 right now, and though I'm trying to get a different experience (grabbed a thief from TDD mod as well as added Keldorn), I've ended up keeping Minsc, Jaheria and Arie in my party again. I might dump Minsc, he's a great tank, but my Cleric/Ranger is so buffed that I don't really have to have him if I can replace him with a decent fighter.
Then there is Jaheria and Arie. The one time I've played all the way through ToB (finished SoA several times), my love interest was Arie, so I know how that turned out. I decided I'd keep Jaheria in and romance her this time, but I just can't get myself to kick Arie out. She reminds me a bit of an ex-gf and I just can't do it! Thought I might kick Jaheria out, but after having her in every one of my other play throughs of all three part, it just doesn't feel right!