Pheace: I'm not much of a dota player but honestly, HOTS had me craving playing DOTA when I play it (not that I ended up doing that). I think in particular it's the lack of the characters being able to do much of anything interesting mechanic wise, it's mostly damage in some form or another. Sure you had Diablo where if you're lucky you toss the player on the other side of a wall, but other than that it was pretty bland. It mostly came down to groups because on your own it's just not that great.

Granted they had some interesting characters with interesting gameplay styles, particularly the specialists.