Novotnus: Shot boss until it dies - stay in the past.
Puzzle based on figuring out how to kill the boss - yes, please!
This. I don't want a boss that has 10x more HP and takes forever to trial & error in a ridiculous dance because I've too low HP or something else.
A boss with good AI and a puzzle around him, preferably, thrown together in sequences is better.
As for bosses in general, I prefer a more linear but flexible difficulty curve rather than easy mobs and than a boss with a cool name and huge model and 10x HP.
TStael: - Scripted boss fights, at any chapter really, like Witcher II that had essentailly only one replicatable linear solution that became uninspiring pretty fast, particularly with the appalling PC "controls."
Haha, I failled miserably on the last boss. I noticed the pattern on how to play pretty fast but it became a drag because it took so damn long to finish him and I made a few mistakes in between and had to do some retries. When I finally killed him I noticed that my Aard, fully upgraded, damaged him a lot more than I thought and I noticed a new tactic to avoid being hit so I could basically have won in a few minutes instead of the 30 minutes it took when I finally defeated him.