Your in a boss fight, you whittle him down to a sliver of his health, then BAM!, you die. You restart in one of two ways: Somewhere in the level before the boss, or right before the fight starts. Either way, you have to do everything over again until you win.
This is not fun. At all. It is, and never was fun. Please stop doing this. I suggest the Infamous route, where there's checkpoints throughout the fight. So when you restart, his health is close to where it was beforehand(Checkpoints would activate when 1/3 of his health is lowered, and continue from there). Much like Infamous.
And another thing, don't force me to watch the cutscene with him right beforehand every single time. Its even worse if its unskippable, which it usually is. For this, go the Sly Cooper route, where you don't show the same freaking scene over and over again, but take us right into the battle.