If I understand correctly, the first SC2 part is 30 missions which is the same as all 3 parts of the original SC (10 levels each). I guess I haven't played a ton of RTSs but 20 hours for 1 play through of the single player campaign is pretty standard for me. Also as far as DRM is concerned I was told it would be similar to steam in that you have to "activate" the game once (if you don't buy it online) but after that you don't have to play online. They will be adding achievements, multiplayer and friends contacts, ect, to try and make you want to be online but it's not required.

That being said this is all hearsay until the game comes out and further information is available, but from what what I've Kotics "assyness" hasn't extended to the Blizzard side of acti/blizz yet.