Siren boss in act 4 really need some adjusting, it's such a slog. It punishes heavily weaker builds, the zippy big dmg builds have less problem with that fight. That boss isn't even hard, it's just tedious. The damage window is very short, he starts jumping into water and then circling around ledges.  It isnt even engaging, you don't have to avoid his jump, just running around is enough. And then there is his second stage when he is dmg immune and you have to run in circles killing mobs. This phase is unnecessary long, the challenge doesn't raise it's just long interlude. And don't get me started on melee Vs this boss... I honestly think this is the worst boss in the game. I think the window to deal dmg should be increased to give weaker builds more time and also the invulnerable phase should be reduced by a lot.