Most games have bosses, and most of those games you simply have to despense your ammo onto it until it stops breathing. Either that or it's a long hard and annoying game of hide and seek (hide from its weapons) until you manage to exploit its only weaknessess. Sometimes these can seem like a task, but every blue moon you get a game where its bosses are fun to beat. Gameplay that's initiative or challenging that still keeps the fun factor alive.
I remember Conker had some great boss battles. While you had to pull off the same thing three times (and it was always three times) some of the battles were fun, for example, cleaning up a giant singing turd before flushing it down a toilet. A few of the bosses were a pain to kill but usually enjoyable just to fight. Bioshock as well (if you classify Big Daddies as bosses instead of really hard enemies), the Big Daddies were fun to kill. You could stare them down and wait a bit before getting ready. It was fun to booby trap the place up and wait for just the right moment before shocking him and letting the bee's of war loose onto him.
I remember Conker had some great boss battles. While you had to pull off the same thing three times (and it was always three times) some of the battles were fun, for example, cleaning up a giant singing turd before flushing it down a toilet. A few of the bosses were a pain to kill but usually enjoyable just to fight. Bioshock as well (if you classify Big Daddies as bosses instead of really hard enemies), the Big Daddies were fun to kill. You could stare them down and wait a bit before getting ready. It was fun to booby trap the place up and wait for just the right moment before shocking him and letting the bee's of war loose onto him.