Not at all. There's something like 835 individual moons in the game, not easy to complete at all. You could go through 64/Sunshine/Galaxy in 5-10 hours if you want, it's the way 3D Mario always has been. Once the story finishes the real challenge starts.
The boss rematches postgame, as well as the dark side of the moon and the 'true final level' you unlock at 503 moons, are absolutely no easy task. I'm at around 300 moons now and I'm having trouble with a bunch of moons. The main story's easy, sure, but the game's not easy.
With that count it seems you've blown through rather quickly, I had around ~256 when I finished the main story.







