Well, yeah...
I mean, the Galaxy series were truly imaginative. The level designs were very creative, varied, and fun. The series brings the most polished 3D platformer to date with amazing shifts of perspective. The gravity mechanic of Mario Galaxy truly makes everything amazing, as Mario's jumps and platforming challenges often change in regards to the size and shape of the planet. Not only that, but it shifts your perspective of not only it being a flat plane, but of something with even more depth. Going to other sides of the planet truly makes you think differently of 3D platforming. The Galaxy series has some of the best graphics of any game, despite not being in HD, plus they truly take to heart the theming of the game. Character designs was great, and varied, and added new and old creatures alike to Mario 64.
The only thing that's sort of disappointing, is that there aren't many exploration based levels. However, whenever these levels do occur, they are extremely well made and Fantastic. The whole rest of the game though, is nearly perfection.