Mad God is wet and creepy (affectionate). I loooove stop motion animation and physical effects, and Mad God is very clearly a deeply passionate labour of love. The stop motion is so good that at points it really looks like real people and machinery, which is pretty mindblowing. The imagery, music and meandering 'plot' all drip with atmosphere and it's very clear that Mad God is more of a visual splendour than a coherent story. If I had to guess, I'd say it's about the pointlessness of war, specifically World War Two.
The one thing that kind of lets down this movie is the inclusion of real actors greenscreened into some shots. They almost always look awkward, weird and kind of cheap - like a channel awesome movie special effect, which is a pretty steep downgrade from the frankly breathtaking cgi. There aren't many scenes that use real people and not all of them are terrible (the long-nailed priest is pretty good), but I wish there hadn't been any at all.