Okay, some impressions!
Firstly, the single player is AMAZING! It's a completely different experience from the multiplayer part, the mission objectives are very diverse and refreshing, the upgrades, and research are such a refreshing note! Can't wait to reach the final missions, with the inevitable showdown against Mengsk and Kerrigan.
Multiplayer is also phenomenal. There's no lag whatsoever, even with a 1,000,000 crowded Battle.net, the matchup system league system works seamlessly, and the races / units seem perfectly balanced thus far! I love smashing opponents economy with my banshees, then wiping the floor with them with MMM.
PS: the protoss was my favorite race in the original, can't get into them in SC2 though, Chrono macroing some slow units make me avoid them so far. And my favorite High Templars have been massively nerfed 
My themeforest portfolio:
