Players of World of Warcraft had been clamoring for quite some time: "We love escort quests! Give us more escort quests! We want a dungeon that's nothing but one big escort quest!" Well, good news, person who doesn't exist and never will -- Blizzard designed an instance just for you!
Hour of Twilight is pretty much one big long escort quest involving Thrall. Dude's trying to deliver the Dragon Soul to Wyrmrest Temple, and a whole bunch of bad guys are trying to stop him. A whole bunch of bad guys with loot. I think that's the part I cared about the most. The loot. Saving the future was merely a side effect.
Getting the loot requires you to put up with a lot -- one of the most annoying fights in Cataclysm, in my opinion. I'm talking of course about the Asira Dawnbreaker fight. Thankfully, though, her shadow priest frustrating silences are avoidable. Sort of.