I have only played through to a bit beyond the first boss, and so far it is amazing, best map I have seen so far. Might not be playing with the best classes for it though (took me and my friend 10 lives to kill the raven summoner) Was really annoying when, if you were not close enough to where they appeared in the first boss fight, they did not move towards you. Later, a huge swarm of 100+ would fly at you and be a pain (kept trapping me against the torches, I couldn't move and they suck down hp fast) Boss health was a bit High, but only going through with 2 people (And I might not be the best Hammerwatch player either).
Other than that, only one bug so far, when you get into the area right after the first boss, it spawns you by this entrance, if you attempt to go backwards, you can exit the map. Just wandering around in the void forever. Might want to make it move people back outside.
Also, some of the spider den exits look bigger than the actual exit is, on outside it looks fine, big web wall that you can go through, but on inside the hit box for the walls is a bit too big (or the opening looks too big). Not a big thing, but thought I would point it out.
So far it has been a great, though frustrating, world. Can't wait to see what act 2 has in store.