I Hate You to Pieces
When introducing your boss to players, do it in a memorable fashion. Who can forget Darth Vader’s entrance in Star Wars? Make sure players get a good look at the villain, that they understand “this is the bad guy” they will eventually fight. You always want to give your main villain13 a “Joker moment,” when the bad guy executes a henchman or some other NPC to show what a truly bad guy (or girl or he-she-demon) he is. This can happen within the game or a cutscene.
Have other characters talk about how bad the boss is before you introduce him. Or give the players information in collectable form like audio clips or data files or letters to warn them about the enemy. This works when dropping hints to players on how to defeat the enemy or boss. Arm them with knowledge along with the firepower. Anticipation of fighting the boss will be greater if players know the fight is coming.
When I was working on a game based on the movie Demolition...