4. Satisfying Victory
When it all comes down to it, after you've spent several hours of game-play and all of those lives, you want a victory that makes you scream at the top of your lungs in that dark cave you've made for yourself amongst three days of pizza boxes. Remember that time you beat Gary for that final time after the Elite Four in Pokemon Blue? After 30 restarts and 100 full restores later? Yeah, thats the feeling you want. That complete elation and euphoria. The victory needs to be sweet enough to make you want to go back and whoop his ass again.
3. Atmosphere
Tense, dramatic and edge of you seat action. Any boss battle needs to have the right atmosphere. Partly down to the music, which should never be overlooked, and also the setting. Their grand entrance is the key to this. A sense of impending doom that screams This is itthe big oneI CAN DO THIS!, whilst you shake your shoulders and prepare for that final test. Baring your teeth, you need that atmosphere to really put you in the zone. Plus their own theme song helps too...