In general, I like events that just have creative monster ambushes much more than the ones that try to have a "character" you interact with. Event NPCs reduce replayability because they get annoying the 3rd or 4th time you repeat the event hearing them repeat their spiel over and over again. If an event is not intended to be repeatable, I don't know why Blizzard would bother spending the manpower to put it into the game.
Also the rewards should encourage the player to seek out events. For the most part, that's not the case currently because elite-hunting is worth more than the average event.