Well, here is the thing (have 2008 Imac) and Dell u2711.
IPS, comes with trade offs just like every other display technology. Not even OLED will be perfect, and people are paying outragous prices for that. The 55-incher that Samsung and LG are launching here soon, will cost the same as a decent car. That's a lot for something that is cool, but not perfect.
IPS, like Plasma have colors that pop much better than what we had before. The viewing angles are fantastic. So it has Backlight bleeding and some of them are prone to ghosting, but in the grand scheme of things they are amazing.
The only time I noticed bleeding was during dark loading screens when gaming. I didn't even notice it watching movies, unless the lighting conditions were completely unacceptable, but the 2008 Imac had so much glare that it was crazy.
Plasma looks better than LCD, but even that has it's annoying quirks. I have a 3000 dollars high end LG 60 inch hdtv that looks amazing. It's fabolous and just a hair under the legendary Kuro in image quality. However, it still comes with freaking annoying image rentention. stay on the same news channel for 1 hour or play the same game for an hour, and logos and HUD elements are stuck in the screen for a while. It sucks, but why would you expect perfect?
stuff is as good as it is. If you took a 4 year old MBP and compared its screen against the new Imac, I think it's clear to see what sort of improvements they have mate to deeper blacks, contrast etc.
As for the glossy. Well, it sells machine in the stores. It is not practical and annoying but under the well lit surroundings of retailers it makes colors pop even more. The older Imacs at least had their color gamut tampered with. increased saturation to make it more colorful. Apple actually designed it to not give an authentic experience, but just make it that bit more colorful. It messes with your brain, but so what? it looks wonderful.
it's the graphics designers who perhaps should go with the Dell or NEC screen, as color accuracy is important. Maybe this is not the case on new Imacs.
TL;DR - It's as good as it is - Louis CK.