1) Only respawn point is right at the beginning of the mission, so having to run through miles of corridors every time I get killed
2) Boff pathing is so bad that I either have to keep stopping for them to catch up, or get to Gul Brun to find they are all stuck on walls somewhere.
3) Gul Brun is far too hard to defeat compared with say the doddle of a mission that S'hariel's Swords was. He's in a highly defensible position that just gets crowded with my boffs if they happen to have made it there. Point 1 and 2 exacerbate this issue.
4) It's just not fun when compared to previous missions.
I like a challenge with the rest of them, but repeated being killed in two shots and respawning at the start of the mission is just plain annoying.