Story line: Very good and original- besides the whole Alien invade worlkd stuff but the stories of the heroes: set up the new WC Heroes emphasis
Balance: UNBEATABLE! Some ppl say 1 race is the best and kills all- not so (besides the new and improved Protoss which i can and will never master!). Terran beat Pro, Pro can beat Zerg and Zerg beat Terran. SC set the precedent of 3 totally different sides with advantages and disadvantages. Comon WC1 and 2, the humans and orcs were the same except magic wise!
Units: Look above in balance
Protoss are unbeatable when it is used in the hands of a vet..... with BW killing the unstoppableness of the Zerg (with all units being able 2 take on the Zergs - medics can heal, remove parasite, Goliaths can hurt Guardians and the spawning of larvae was 3 times quicker than the expansion)
The main incentive 2 play Zerg prior to BW was the use of spells.... especially plauge and co.... now the Terran can counter all speels and Protoss have even better spells!!! At least we got the lurker.... who has a tendancy 2 miss 1 in 2 with its spikes!