Bloody Mary. This was my second attempt and I had to do a ton of grinding because I was like 3 levels underleveled for the boss. Boss is a pain because it takes a long time. Lots of Guild Wars 2 talk going on in chat during the fight.
Dark Twins. This boss was annoying. It's hard to hit most of the time and his stupid friend makes it even harder to hit him while he is actually vulnerable. Having to restart the battle because I fell off didn't help things.
Shadowkeeper. I don't consider any of the other fights in chapter 1 boss fights since they are all normal enemies. This one isn't too bad. Ran into a few attacks stupidly but the fight itself is pretty simple.