the original Turok Dinosaur Hunter had some pretty good bosses
but yes today there is a bit of an issue in this regard. you play Farcry or Dying Light or Dragon Age and there aren't really any mega awesome bosses in my opinion (at least in terms of difficulty).
some will argue back with Dark Souls or Bayonetta, but Dark Souls is the pretty far extreme end and a game like Bayonetta is a hack n slash, and I think people are looking more for good shooters or adventure games with difficult bosses
historically the Resident Evil games had some good bosses. I don't know how/when we might see more awesome final bosses but it is annoying when you get through a game and then fighting the final boss is as simple as hitting the trigger as fast as you can or a/b at the correct times when prompted
