When killing your boss is enjoyable

[Nugoo]

Gilgamesh, from FFXII, and GLaDOS for the same reasons.

My favorite boss fight of all time is Dark Link, from Ocarina of Time. Link's just a lot cooler in silhouette, plus it's a really fun fight if you actually fight him with the Master Sword.

 

[Melaisis]

When killing your boss is enjoyable

Well I used to work in communications, and my manager was a real arsehole. Anyway, one day he and I were working late, alone. Whilst engrossed in his accounts, I grabbed the nearest ballpoint and...

Oh, right.

Personally I found the boss battles in OoT far too easy. The only real novel ones which stick out in my mind are those from the Goemon (MYSTICAL NINJA!) series. Fighting, talking, giant robots/Hollywood actors!? Yes please! Transsexual, cross-dressing aliens trying to turn Japan into the homosexual heartland!? Can it get any better!?

 

[Duck Sandwich]

Dr. Wily in Mega Man 7 was the most awesome (and difficult) boss fight I ever faced. The game itself is rather average, but that fight at the end makes up for it, especially seeing the ending afterwards (it's an awesome ending....well, by Mega Man standards at least).