Titan (HM) is pretty close to being fun for me, but Landslide kind of ruins it for me. I think it would be much better if...

- Landslide knocks you off, you are taken to 1 HP.

- After recovering enough HP, waves of 1-2 mobs will spawn, which you need to kill off by yourself. If you fail, you are out. If you win, you can teleport back into the battle field.

- Upon teleporting in, you will have a brief period of immunity, in case you get placed into Landslide/WotL.

Other than that, I think Titan (HM) has a great mix of dodging/DPS check/music/overall kick-assedness. Extreme mode Titan doesn't even look like something I'd want to attempt, at all... ever.

The Copperbell (HM) bosses are pretty fun, and I enjoy Ash from Haukke (HM) - although his blue spinner things he leaves on the floor are annoying as hell.

I kind of like KB from CT, but that fight can range anywhere from "a ton of fun" to "a frickin' nightmare", depending on your group. Acheron is pretty fun as well.