Personally, AoS died here despite the best concerted efforts of the local store owner, partly due to balancing issues, and partly due to people not caring. That said, WHFB had a quiet following here that never really played it, merely owned it, so probably not the best litmus test.
AoS got a good try from most of us, but it feels too simplistic. I dunno, I'd say it's the perfect game for a new person who wants to get into The Hobby as a whole, before they move onto something a bit more cerebral. It seems to draw from a lot of the lessons GW learned in LotR, WHFB, and 40K, but ultimately ended up with something complete unlike any of them with the gaming flavour of wallpaper paste.
The balance was actually the biggest problem, despite our local being pretty non-competitive. The local store owner and a regular got massively into it, the store owner resurrected an Ogre force and built it up, and the regular got into the Sigmarines hard. They had regular weekly games, and one of them would thrash the other. Then the other would slightly adjust the list, maybe add another unit, and thrash the other. They realised after a month or two that they were literally incapable of fielding comparable lists, because they had no reference on how many Ogres a Sigmarine was worth, or vice versa.
It also doesn't help, personally, that I kinda like the challenge of list-building. It forces me to think and strategise, to a point. 170pts left in my Guard list, do I take a Manticore for some across-the-board firepower, a Demolisher for a linebreaker tank, or a Vendetta for some AA/AT support that I can pop a small squad in. Each of them has done me proud at some point, but it forces me to step back and think how the whole thing's going to work together and how each element supports the others.
The AoS format applied to 40K would result in me simply putting my 15K of Guard on the table every game and steamrolling my opponent. Despite it being pretty fluffy for a Guard army, it'd be a heck of a hollow victory.