To me, SC has always been about the multiplayer experience, since the computer AI really rewarded cautious defense in the past, (a tradition continued in SC2) and the comp never showed or shows the tactical creativity of human opponents. Like many chess programs, (including good ones) it trains players to develop bad habits which would not work in "real" games. Thus, my focus has been on the multiplayer, which now I have actually stopped playing. Why? In trying to develop good Protoss tactics, (I had over 10k wins on the old BN with that race) I lost about 20 matches in a row to Terran Reaper rushes merely in the practice league. I tried static and mobile defense (Z's, Stalkers), rush attacks, and the only response on the boards appears to be early probe scouting which is not possible on maps with obstruction that are in the practice league maps. It might be possible to test some strategies in the regular league, but if the player tries to skip practice for ...
