I've experienced this in a ton of games. Luckily it doesn't necessarily bring any disappointment alongside with it. If I'm mostly interested in the story of the game I don't really care if the game and bosses is a breeze. If I want a challenge then I might get disappointed. I just finished the first playthrough of Nier: Automata and that game gave me mixed feelings. It started out rough then got easy as I grinded it out a bit. Because the easyness was a reward because of the grind I didn't mind.