I'll answer your question with another question.
Does it really make a difference how difficult they are? If you killed everything but that boss, what will you do next? If I tell you it's a pain in the ass and you'll spend the next four weeks wiping, does that mean you won't try it? If I tell you it's a piece of cake, will you believe the cake isn't a lie?
In general, raid end bosses are typically tuned to be equivalent in difficulty or sometimes slightly harder than the easiest of heroic mode encounters. That would be the response most would give. And that's how they design it, so you know when you kill the end boss you are ready to start attempting the next thing, heroics.
Well in that same regard, if you are killing everything else in the instance, then you're ready to start attempting the next thing, the end boss.
"In anything, if you want to go from just a beginner to a pro, you need a montage." /w TankSpot WTB Montage for Raiders.