Is it worth it? How much time and effort do you really want to spend playing a game?
This game is obviously built for multiplayer, and more precisely, it's built for competitive e-sport multiplayer. In order to play this game well, you have to master the minutia. People post replays of their losses on the forums so that others can critique them. The critiques usually focus on absurdly minor details, but that's what this game is all about-- the tiny details. "You expanded four seconds too early"; "You missed one larva inject (out of 25)"; etc.
The ladder matching system is broken. In one match the system paired me with a player that didn't know what he was doing, and I won in 6 minutes. The next match was against a player who was two leagues better than me, who crushed me in 12 minutes. So rarely do I ever play a match against an opponent of equal skill.
After you've played about a hundred ladder matches, you being to realize that every match is fundamentally the same. Your opponents use the same two or three strategies: For example, when you play a protoss player, he will either 1) zealot rush; 2) mass void rays; or 3) dark templar harass. That's it. That's what they do.
After a while, i realized that I was playing the game not because it was fun, but because I wanted more portraits, and I wanted to get promoted to other leagues. That kept me playing. It really is addictive. As soon as realized that, I stopped playing, and I haven't played since.