I don't think 10-15 min for a boss fight is too much. There was a time when booting your computer took that long lol :-P. Well just kidding but as long as the fight is engaging... OK Iron maidens is a bit dull but I would like to see more boss fights that go longer and maybe have some cool scripted specials.
Boss fight isn't that long if you are a good player get in there get the kill and stop complaining
I like a long boss with many different phases. Feels more epic. Feels more an achievement (literal, not an achievement in WoW). As a DpS, I never get bored, there is always room for improvement in execution, DpS, damage taken, etc.
It's long but it's fun.
Much better than fucking Galakras.
This one was my least favorite fight in a very long time. 12+ minutes of killing trash that spawns on a set-in-stone timer. So if it's your farm night and you have good gear already, you afk 30-50% of the time. God, i hated that boss, it always made me almost fall asleep.
Longer fights means there's more time for people to make mistakes. On the complete reverse-end of the spectrum, a fight that took 5 seconds would be utter crap. Some fights are about performing very well for a short duration, and others are a test of the player's endurance. Iron Maidens itself is boring, but that's a flaw with the encounter mechanics; not the duration.
Fight is boring and the voice acting is horrendous
Roboctopus of STAY MAD - Sargeras
http://staymad.enjin.com/
I really don't like fights that start slow and have a first phase that is essentially a waste of everyone's time. The best example of that was P1 of Ragnaros in FL (at least I had some fun there by proccing the traps but otherwise nothing happened there). Imperator is in the same category, it feels like the fight is dragging out in the easy parts. Repeating the same easy phases for 6-7 minutes each just to determine tactics on the last phase starts to really exhaust you.
I don't like really long encounters, however I really don't like long encounters with a "raid wipe" type mechanic at the very end. Nothing sucks more than spending 10 to wipe to a sub 20 bezerk or what not. Those endings should be reserved for short encounters.
Garrosh phase 4 is a perfect example. Neat idea, but after a hundred pulls to kill him in phase 3.. only to die a few seconds later to an iron star...uggg
5-7min is about the perfect length.