Diablo 3 is an excellent game on both PC and Console. The balance changes that they made were a significant improvement, and I'd consider the current D3 one of Blizzard's great successes as gameplay goes. It greatly expanded on Diablo 2 with completely new and fresh mechanics that have been an absolute blast to explore as a gamer. It was a little too unforgiving before those balance changes, with bumpy progression and a difficult skill cliff, and overly reliant on the auction house (not intentionally in a gimmicky way; it's just how it turned out when AH prices dropped ridiculously low due to surplus supply). It's great now though. Diablo 3's artwork is beautiful, and to achieve it they developed an innovative new style which they presented at GDC 2012:
http://gdcvault.com/play/1015306/The-Art-of-Diablo
(This is what I mean by "fresh" by the way: something new and interesting that you haven't seen before, even in an industry that tries it all. The painterly style was definitely fresh, and even in the years since then I haven't seen an imitation. I suspect it's too technically challenging, requiring a custom engine and a different way of designing environments.)
I guess you can tell that I'm a fan. I think you hit on all the things that Blizzard does well: repeatable without repetitive, simple but deep with high skill cap, where you discover new things about the game mechanics yourself over time. Diablo 3 is especially fun because of its multiplayer coop. It's great to get the S.O. or friends in the same room and collaborate, especially on console.
Diablo 3 has continued to trickle out new content over time for free after its expansion, Reaper of Souls, which has further helped to improve balance and make it interesting. I wish they would release more content though, since the game by its nature is ultimately repetitive. (Hard to justify financially with no recurring subscription. I would be very happy to pay for one if it meant more content!) There are rumors that Blizzard will release another expansion, which I will be super excited to explore if they do. I personally feel it's one of the best games ever made, and definitely the best action RPG. I don't think this quality of design can be boiled down just to a list of things they do well. It's definitely something more than that. They have an internal compass of what it takes to make awesome games, and they're willing to wait and iterate on their development as long as it takes to get there.
Heroes of the Storm I'm skeptical of. It's much more directly a rip-off than any other Blizzard game, and I haven't seen much fresh or new come out of it yet.