HoTS is without question the best of the moba's. It gets you into the action quicker and the feel of the characters is very smooth, more so than any other moba except maybe league. While the pro scene was nixed from HoTS there is still a very competitive player base and is still just as skill based as any other moba regardless of the bs calling it "casual". The fact is that the skill ceilings on moba's are inherently infinite so there is no such thing as a casual moba. They're only as casual you want them to be. There is no stupid ass laning phase where you have to last hit minions for 15 minutes before you get strong enough to actually be able to play the game. In HoTS games typically last around 20 minutes and there's no getting stuck in ridiculous 60+ minute games. Idk, I've played them all and HoTS is definitely the best.
The most common negative that is brought up about it is that you "can't get fed and carry a game". This is mostly false. While you can't carry as hard as you could in other moba's if you get fed out of your mind, a single player absolutely can carry a game very hard. However, it is definitely the most team oriented of the moba's and there is a significant emphasis on team fighting and fighting over objectives.
Also, the best part of HoTS is that there's like a dozen different maps that are mostly all very well designed which keeps the game feeling very fresh. No repeating the same exact map 10000x over and over.