Sindragosa is the worst fight in the game at the moment.
I think I might hate the LK worse, but Sindragosa annoys me in such a similar manner that it's kind of a toss up. Arthas has the most mind numbingly long/boring Phase 1 I've seen in a while. The only people who might face a challenge in Phase 1 are the tanks and healers, but a couple pally tanks and a good Disc Priest largely trivializes even that. This is followed up by Phase 2, which is a pretty nasty stopper. So, basically, our early LK failures have generally looked like this:
1. Buffs/Preparation/finger pointing. This might take just short of forever.
2. Nearly a full minute of lore bullshit that will get REAL fucking old by the end of the night.
3. A few minutes of boring tank 'n' spank and light add management.
4. 1 minute of phase transition. You're probably still bored at this point, but hey, at least it means Phase 1 is over.
5. Phase 2! Life gets interesting... for about 20 seconds. That's because Defile has two settings: Harmless and Wiping The Raid Because Someone Tunnel Visioned. Go to step 1.
Sindragosa is pretty much the same way. Couple attrition phases, phase 3, wipe, wash, rinse repeat.