Hi! I'm one of the players in this game, I figured I'd chime in some thoughts from the perspective of the players.
I've had four characters up to Xanesha. Unfortunately she managed to crit me and did about 80 damage, which was one-shot-dead for me. This isn't the first time, though; I lost one character to Eryllium, one to Gogmurt, and one was purposefully retired before another grim death.
As a player it feels very unfair to fight most of these big-bad monsters sometimes. When we fought Eryllium, she simply flew up higher than we could hit her and started raising zombies, which resulted in the entire party fleeing the dungeon and walling it up; her regeneration made it even more of a painful chore to fight, too.
Along with that, it seems that even some simple things are just decimating us; while in the fields with the ghouls, we got ambushed by four of them, and they paralysed and mauled every single party member with ease. We've had to homerule that creatures can't outright coup-de-gras someone with natural weapons because otherwise we'd have been TPK'd.
Oftentimes we're a very mixed party. While we do have a tendancy towards big-hitty-smashy dudes, we will occasionally do some serious scouting, stealthy dungeons. Currently we're fairly ballanced (or were, at least). We've been with and without a proper cleric, but either way it still seems just as difficult to survive any encounter, and the same goes for ranged characters. We've done proper reflecting on combats and situations, and me and another player even made complimentary characters specifically designed to deal with situations we've encountered, but it's still insufficient. It's got to the point that it's more realistic to entirely ad-lib your backstory and character concept because you'll probably die in two sessions anyway.
All in all we've all been pretty bummed out about our combats. We've been playing Pathfinder in some form for many months, we do know our system fairly well, but we've just not got a break at all from the constant deaths.
With 25 point buy systems, fast track XP and large player experience, we're still being floored by the simplest of monsters.