It's always had it's warts and drawbacks, but 5.4 seems to have completely broken it. I haven't had a successful Wing 2 run in a couple weeks now; if a group makes it to Dark Shaman, that's as far as it usually goes. One hour queue, plus two hours for Dark Shaman, then waiting another hour for tanks, then another hour wiping on Nazgrim. Five hours to down one boss... that's a failed system. And it's a common thing now.
Sure, LFR works in a pre-made, but that's not really LFR, and you might as well do flex at that point (unless you're desperate and going for a tier piece or trinket to hold you over).
Tonight we wiped 3 times on Juggernaut (before I left, not before he was downed) due to the tanks being all sorts of screwed up. The DK tank had zero enchants except for Windsong. Pvp gear. And no one could/would kick him. My timer is maxed out (don't get me started on WoW punishing the players who do the right thing with high kick CDs). It's like every fight is Lei Shen right after Wing 4 opened, but worse... and it's not the fight mechanics that are the problem. I really hope Blizzard's response to this isn't to nerf the instance or claim that it's because the fights are new, because catering to people pulling 10k dps (and DK tanks with Windsong) is not the solution.
The solution is simple. LFR needs to be gated, period. A higher ilvl requirement for each wing that gets opened wouldn't hurt, but it's not necessarily a fix all by itself. Proving Grounds would be a perfect lock. Wing 1: open to those who have completed LFR ToT. Yes, all of it. Wing 2: Silver Proving Grounds for the spec you signed up with. Wing 3 and 4: Gold Proving Grounds. On top of that, how hard would it be to implement a gear/gem/enchant check for LFR? Yeah, I know some tanks like to run with DPS gear, and in Flex/Normal/Heroic you still could. In LFR, it shouldn't be left to chance... because odds are, that tank is in dps gear not because he wants the extra threat/dps, it's because he's a lazy or incompetent douche who wanted a fast queue.
LFR was a really cool and sometimes useful concept, but it's gonna die a nasty death unless Blizzard implements some controls. Let's be honest, the entire concept relies on the fact that there's experienced, geared players pulling the groups through. When it becomes so painful that those players stop running it at all... Hell, I'm not exactly slumming it when I run LFR; I'm a moderately competent player, probably average (Flex is fairly easy, heroic would probably be beyond me) and if it's gotten so bad that I'm not willing to set foot in the raid finder crapfest anymore, something is seriously wrong.