Boss battles, really only needed in RPGS or RTS games, where its something your building up to/against in the end. For FPS bosses should GTHO my space, cause when you have some games which are pretty realistic like... some ww2 shooters like MOHAA you have some of the older games where you fight a final boss which takes about 500 shots from your most powerful gun.

But in rpgs, when you fight the power boss at the end which you find out slowely through the game attacked your small home village killed every on in it, then slowely prods you through out the game, now those are bosses.

As for mini bosses, I'd just prefer dungeon bosses and party bosses where they are harder to kill but you get good loot from it.