another cool thing about Sylv (I guess that goes for any siege hero tho) is how disruptive they can be so you always have to have someone on them, sometimes 2 ppl which makes it easier for your team even if you arent in TFs.
Anyway im really liking dedicating more time into 1 character up to 10, theres that nice reward with the 2 boxes and the 500g at the end, and you put in a nice amount of games to really get a good sense on them, both to learn them and especially to know if you like them or not. Actually looking forward to resuming Kael'Thas after Sylv.
edit: to the question in hand, in my 2 year absense from HotS, I did not touch another moba. I had no desire then to try or "upgrade" to a "better" moba, nor do I now, or ever really. HotS was the perfect storm of a universe I know very well (kinda how I played 2k hours, yes, thousand) of Marvel Heroes mostly for the universe, but I dont care to play the other Diablo-style games which im very sure are better games (your path of exiles, grim dawns, etc), and also the shorter games and the shared xp. Its really a moba made for me I guess.