Personally I wouldnt buy it, unless someone paid me to.
The main thing with the game is you can do what you wish with it. It was intended to build things/sets from valve games and use them to play with/film on.
However its flooded with things like RP (that video) So there are many stupid sides to it.
Things like prop hunt, murder, and hide and seek can be fun (WITH FRIENDS!!!)
Expect to find people who should shouldn't be trusted with something sharper than a crayon on there. There are a few decent people, not many.