I have no problem with tough bosses. I really don't. The problem with the Kayran is that it is a cheap boss, and it exploits every weakness in the combat system. The dodging is a bit unresponsive, and the fight is based on dodging. The hits are timed, but sometimes the Kayran gets a hit in-between. I would sometimes even get hit when hitting a tentacle. It wouldn't be a big problem, except each mistake gets me killed. The vast majority of my deaths were cheap, and that's why it was so enraging. I die in games a lot, especially because I choose tougher difficulties, but dying is rarely this upsetting.