I'm with the consensus on this one. Yes the original was great, but the second one definitely improved on it and the story was actually quite fresh. Brotherhood was okay-eish and Revelation I never even finished, because it just got meh... With ALL the extra things you could do in Revelation it just got a bit much for me.
Hopefully 3 will return to basics and not overwhelm you with things to do. I can understand it increases the replayability, however repetition is not a good way of achieving this. Get bored of doing the same thing, over and over... Here's looking at you Diablo III.