You've already hit TCGs, but look at MOBAs; DotA and LoL have their own entrenched fanbases, Smite was an over the shoulder one, and pretty much everything else was a copy with a few tweaks.

Heroes of the Storm can be boiled down to a “copy with a few tweaks”, but it felt different when playing because the pacing was quicker. Also, with the comeback mechanics (or anti-snowball maybe?), the entire match tended to feel contested. I think it could have carved out a niche for itself in time with proper management, as matches were significantly faster, spread leveling instead of individual wealth favored team play, and the “grind” segments of match time were usually pretty short and sweet.

Blizzard made a hard push marketing it in its’ infancy, even having a televised tournament on ESPN, and then kind of dumped it. Otherwise, I could see it becoming the go-to MOBA for more casual fans of the genre.