Boss fights have not been very popular in the modern age of video games. They've been relegated to easy to design fights with a boss that swings at you a couple of times in a very predictable way. They also have immense amounts of health points, giving the player the illusion that the fight is actually very difficult.
However, games that have boss fights with interesting behaviors and attack patterns challenge the player in a more dynamic way then just having them chip away health for forever.
Titanfall 2
Throughout the single-player campaign of Titanfall 2, the player faces against a couple of bosses. These bosses don't have massive amounts of health. They just all have very distinct personalities and have very different and interesting attack patterns. It's also extremely unique where you fight each of these bosses also, making for an even more dynamic experience.
Dark Souls
The bosses in Dark Souls are large, unique, and require the player to learn how they move and what their weaknesses are to take each one on. It's up to the player to discover the pattern needed to take each one down and they make for complex and rewarding kills when you do finally master them.
Star Wars: Knights of the Old Republic
At the end of the game, spoiler alert, Raven is forced to confront Darth Malik. The build up to this fight extends throughout the entire game. Darth Malik continuously heals himself using the force to drain the life of the defeated Jedi in the chambers around the room. The player has to learn to defeat Darth Malik while destroying the other Jedi. It creates one of the greatest endings to a game.
