It's not exactly rare for the final boss of a game to be a bit lacklustre. If you've done all the optional extras the game provided you with before getting there, chances are whatever ancient evil or world-ending force you have to fight against provides all the challenge of a slightly damp linguine strand.
And, even if it does, you're likely very, very prepared for it. All the hordes of valuable items and power-ups that you've been holding on to (and refusing to use even when you needed to) are for this one battle - and since it's the final battle, you suddenly have full license to chug every revive you've collected along your way.
With all this in mind, there are plenty of times where your biggest challenge was actually the strength of some of the regular enemies you fought along the way.
Despite the fact they were only supposed to be stepping stones on your route to this big bad, when you look back it actually seems like they were far more dangerous - be it because you were ill-prepared, or because they were downright powerhouses.
Sometimes - in life and in video games - your greatest challenge isn't always what you think it will be. Sometimes it's just a lizard.