P1na: Actually, I think the monastery boss (wilhem, IIRC) was probably the hardest boss in all game, unless you count the final boss without freeze and/or blood steal. So no surprise to ragequit there. That said, I recall going back to the normal monks on the first level to keep feeding on them and recharge my blood levels.
Monastery boss was named Mercurio, a significant name with quite some lore behind, in the World of Darkness theme. In bloodlines he was the friendly ghoul in the beginning, though, in redemption he was an enemy, even if Cappadocian clan (allied to the Brujah at the time, supposedly at least) and the game's very first boss.
In vanilla Redemption (1.0 version of the game), he was the hardest fight in the entire game, indeed, for three reasons:
1) Had advanced disciplines dealing insane damage (plague wind).
2) Had lots of hitpoints and no way to freeze him (prison of ice), drain his bloodpool (no theft of vitae at that point in game, feed doesn't work on him either); also he could feed on you even if you wore the Neckguard item.
3) If you used awaken upon Christof's or Wilhelm's torpor ("dying" from enemy) and weren't fast enough to drink something and use blood healing momentarily, you would be one-shotted by that boss (plague wind or it feeding on you) and fall in torpor in just about 1 second, in succession of your being freshly risen.
A very dangerous fight. The one and only (official) patch, among other things, nerfed him down.