By far the most stunning aspect of Dota 2 for me is what Icefrog did in terms of balancing. I'll try to explain.
Out of 107 heroes only 8 heroes were not picked at TI4 and just one (if I'm getting this correctly) at TI3. There are a great deal of general strats, ways to build heroes (items and skills), ways to lane (we sometimes even see dual mid), and many gimmicks (e.g., lvl 1 rosh, ancient creeping heroes, etc.). Teams have personal flavour in their style - both strats (death ball push, 4 protect one, 3 core, mid carry, carry supports) and picks (signature heroes all around).
Heroes/strats are generally counterable, with a few all-round too good heroes but it's usually taken care of. I say counterable because for example there was a huge difference between BO1's in the groupstage and BO3's in the main event - the champion almost didn't get out of the groupstage on BO1's where drafting is done with little reaction to previous games. Also teams get figured out pretty quickly if they use the same (smart) strategy for a long time.
The meta (game trends etc) shifts drastically from year to year; captains can shine creating new strats (e.g., Alliance winning TI3 with "rat doto" - kinda like tanks in WC3) while others fail to adapt (e.g., Na'Vi which are similar to Grubby for WC3) to current patches - which aren't just minor tweaks.
This state is for me the holy grail of balancing. It's not like SC1 where the three races balanced was a work of art, but more in the sense of teams being able to play their style without worrying about balance that much. Also, plainly speaking, the amount of viable shit is really impressive.
All this while in WC3 there were units, even heroes almost never used, or in SC2 units which don't fit in the game. While great games, they don't offer that much in terms of variety and you can't really innovate.