>>161The campaign is 15 missions long. It's split up evenly between the three factions but you cannot decide which faction you'd like to start playing as, since they're in chronological order.
The campaign feels more like a puzzle game compared to skirmish or multiplayer, as there's quite a lot of scripting involve. The campaign missions also double as a tutorial, so you're given optional tutorial messages to read whenever you build or train something for the first time. This doesn't mean that the campaign babies you. It trains you to keep on your toes, even on easy. My favourite campaign mission so far is the mission I mentioned in
>>148 , because it really makes you aware of how dangerous the goo can be.
I found the missions where you play as the goo themselves to be most challenging, because they're the later missions in the campaign, and also because of the goo's different way of working compared to the other 2 factions.