Besides harvesting resources and building shit, you have to dive for cover and make sure you have one or more established shelters during the night. At night, zombies, skeletons, and exploding green penii come hunting for you.
Some crazy kids have done some outlandish things with it. I watched a video on youtube where someone is building a 1:1 scale model of the USS Enterprise from the original (I think) Star Trek series. They've got most of the skeleton there and it's truly an awe-inspiring video.
For good measure, here's a model of NYC
It's more a game for the creative types with lots of time and patience, but it's so easy and user-friendly that it seems like anyone could get something out of it. The sense of scale is kind of unprecedented. The way people are creating whole worlds reminds me of Inception.