Pretty much just building and surviving but there's several maps so once you clear out one you can pack your shyt up and move your squad to a whole new map and clear that out as well. I'm big on single player campaigns/story but while I do wish it had a more "fleshed"
out story, it's understandable that it doesn't. This game with a legit campaign would be AAA status, and deservedly so. Like pres said it's the gameplay loop that has you stuck. It's hard to turn the shyt off once you get started cause this game makes scavenging and building fun as fukk.
Also, I play in the dark and always find myself doing missions at night so it's fukking terrifying and I love it. Zombie noises are A1