I thought this was a masterpiece. It scared me in a way and to a degree that no other movie has. I wouldn't call it 'fun', but it is really _really_ effective at being frightening in some innovative ways.
Skinamarink bypasses all of the defenses your adult brain might have against horror movies by throwing out the genre conventions you have built up an immunity to and squarely targeting your vulnerable inner child.
The movie doesn't just depict kids who are afraid of their home that has been made horrible by darkness, it _simulates_ being a kid who is afraid of their home that as been made horrible by darkness. I'd venture to guess that everyone has been afraid of the dark in their own house when they were young. I know I have, and this movie did an excellent job of dredging up that old, sunken childhood terror.
There are lots of long, still shots in this movie because a scared child in a dark room will hold perfectly still to stay hidden and they will stare intently into the darkness looking for threats. Such long, empty shots would normally be really boring, but I found them really gripping in this context. I felt like a child trying to hold very still staring through my own imperfect, grainy vision into the darkened, malevolent rooms.
The movie has hints of a plot, but I don't think you are given enough information to truly piece it together. In the end, there are a couple of kids, some absent parents, and a haunted house. All you can really know for sure is that you don't know what's going on and that's frightening in itself.
The long shots of more or less nothing, the thin plot, and the lack of conventional movie touchstones combine to make a movie that has turned a lot of people off. It's difficult to watch in a number of ways, but what some consider this movies faults (the slow pace, the violence against children, the inscrutable 'artsy-ness') I consider virtues. I think they add to its overall effect of being scary as hell.