Got the Necro levelled up and had a bit of a play with with the legendary affixes to get it semi geared. I went pure minions and not one of the busted spell caster builds that are coming up, it still felt very over tuned for those early levels though.
I've been finding the minion AI to be a bit hit and miss, the aggression and target priority seems a bit all over the place at times. Sometimes they won't engage enemies that are at close range, unless they are hit by them or initiate I an attack first. Other times during the events I find them running around everywhere when I want them to stick close and be meat shields. I often see them switching targets too, there could be an elite that they swarm and start to melt, but if another trash mob attacks them they suddenly all aggro to that instead of finishing off the elite. Certainly needs a bit of tweaking or some behaviour options added in there to make them a bit more predictable.
It probably will be a purchase from me, but not right away. Nothing I've played or have read from the guys leaking the endgame/paragon details really stands out to me yet, all these games tend to take a little while to cook and hit a nice balance, plus if there's seasonal content I'd more than likely be playing that exclusively anyway, so there's no loss for me to watch from he side lines for a while and see how things pan out.
I think it will be better than D3, but hard to say where it sits with all the other games already out there at the moment. If they stick with it and come up with some fun/creative content to experience or even add each league then it will probably be solid. If it got the D3 treatment though I'd get worried for it pretty quickly.