I don't know about many of the unfinished parts of PoE, because I haven't been in the beta for long yet - but I totally agree with Kabraxis on the part of polishing the game before releasing it - and improving it later on.

I think lack of support is one of the main reasons why games fail. It's a pity to see how many promising ARPGs were finally left unfinished - usually due to a serious lack of support on the part of publishers.

D2 is a fine example: IMHO D2 is still the best ARPG around and that simply because blizzard decided to support and improve it over 10 years. Pre patch 1.09 D2 sucked big time - and I couldn't care less about it. But then Blizzard got smart and created some real coop-gameplay-experience.
(Not that I have too much hope for D3 though...)