It can be blown through pretty fast if you ignore everything but the main questline, and the game overall is a touch on the easy side on the normal difficulty. Next level up is better, but the controls for your fart powers are so finicky at times, that it may not be worth the headache, but if you do all the side stuff, it lasts a fair while. I am about 60% through, looking for everything, after about 15 hours playtime.
The engine also sets up the DLC, that from what I have seen are going to be like standalone "episodes" that look pretty promising.
I started this as a dl, but will likely buy it since I have enjoyed it a fair bit today.
My wife on the other hand, is horrified.