I would mostly only complain about server instability. Mal'ganis is a very highly populated server. If wintergrasp is going on any time in the afternoon/evening the server usually lags horribly or crashes.
My guild was on a really good Immortal attempt recently. We'd done 3 wings with no problems. We saved the easiest for last, and we were all excited cuz we knew the rest would be a breeze. We pull Anub, lag out, disconnect, log back in and lots of people are dead. Such a waste. Some people called GMs and the gms said "if you're lagging it's probably your addons. disable them or reload your ui" .........
Oh, I guess I'd also like to mention I hate how GMs are so useless. The only way you can ever get anything done when you have a real issue is to say you want to talk to a senior GM.