There are a lot of boss fights in Wow that I would consider lightbulb fights. They're those fights where you seem to be pounding your head into the wall, but you just can't seem to kill the boss. You get to the point where you feel like you just can't take another wipe, but yet you still do. It's the fight that has become the bane of your Wow existence. It makes you want to stick puppies in the microwave. You're contemplating cancelling your Wow account because of this one boss, and then... you kill it. Furthermore, you go back in the next time, and you 1-shot it. That's the lightbulb fight. It's the moment that something clicked, everyone has finally figured out everything they're supposed to do, and it's as if a lightbulb has finally gone on in everyone's brain. The fight is then practically farm status because it's become so "easy".
There's a few lightbulb fights that are like this in World of Warcraft. I would say that Shade of Aran is kind of like this. Once you figure out all the things you have to do AND deal with the elementals... it's usually cake-walk. Netherspite is another one because it's so hard to stand it beams. High King Maulgar: positioning. Magtheridon: clicking (although do people still have problems with him post 2.4 nerf?).
And now, to add to that list, Al'ar. Well, maybe not completely "easy", but still. Last night, we walked in and smacked Al'ar upside the head on our first shot. That's only the second time we've killed him. And yes, only the first attempt after our last kill. We still had a few deaths by the end of the fight, but the whole thing felt very controlled and when somebody died, it was easy to assign another person to the position. I doubt our gear has improved that much in the week and a half since our last kill... it's just that the lightbulb went on.
Side Note: My DPS is now officially sick. I'm still learning the best way to use my super combo of IV, trinket, AP, AB spam. Originally I was told to use mana gems/pots in the middle of that, but I think my quick evocation (when IV is still on) will probably take care of most of my mana. At any rate, if I can get that one down and using it every 3 minutes, I'll easily top the charts.
Side Note 2: Went with a guild group into ZA last night, and pretty much pwn'ed the first 4 bosses. Got the Hexlord to about 20%, but then we were all getting pretty tired. It reset this morning, so maybe we'll go play again tonight. (We'll see when the SSC run ends.) Also got 2 of the timed bonuses. So much fun to have runs that are fast paced like that.