My friend bought Sc2 and he shares it with me, and if you are competitive and enjoy RTS (I played a lot of Ladder WC2 and Wc3 TFT, also C&C Generals and Red Alert 2) then get it for the ladder. If you enjoy custom maps get Warcraft 3 or Sc2. Although WC3 is dying, imo from all the hosting bots.
Sc2 is a very creative game in both the ladder matches & custom games. For instance, one map is like an all out free for all where you get resources stupidly fast and have to dominate them before they dominate you. A huge clusterfuck of units on the map as you can imagine. That's swayed more to modified ladder (By the way, ladder means ranked. Just basic, 1v1, 2v2, etc).
Another favorite of mine are their zombie survival maps. Quite hard and fun.
They have a huge variety in the custom map part of it. Zombie survival, tower defense, merchant+fighter, tug-of-war, DOTA style (If you played wc3, hon, LoL, bloodline champions, etc), and more. Hell, someone is even making an MMO inside of the starcraft 2 map editor (And ironically naming it World of Starcraft XD Link
HERE)
Overall, it is a fun game if you enjoy random custom maps or competitive (And I MEAN competitive, fucking Korea owns Starcraft) traditional RTS games.
Tl;dr, i'd get it. or get a friend to buy it for you. Either way the online is worth it, plus the single player, although short, is actually offers quite the immersion and a good story. Although hardcore SC/BW fans would say its crap, I still loved it.