I had done all the quests on Icewind Dale on my first playthrough, but that didn't stop me replaying it 3 more times. You can still do the same quests differently (i.e. role playing as good vs evil char), choose different party, factions, ending etc. I like playing PC RPGs as neutral good, rational character during my first playthrough, then as homicidal maniac, who kills anything that moves, on the next one.