Super Paper Mario
This is one of those games that give you an “oh wow” moment the first time you play. That moment comes from the new form of gameplay of switching between 2-D and 3-D. Oftentimes to advance within a level you have to switch back and forth to find your way around or to find what you need to interact with to change your environment.
It’s more than just a gimmick though; when you switch never feels extraneous or disingenuous to the levels.
Another reason I love the game is its style. Each world has its own theme. For example there is a Stone Age themed world, an outer space themed world, and a world based on Hell. My favorite themed world has to be the blocky 8-bit one. It is a homage to NES era games and to Super Mario Bros. specifically. The whole game is full of in-jokes and references to other games and genres.
The game is supposedly a hybrid Platformer/RPG but the most compelling part of the game to me is the environmental puzzles. The 2D/3D dynamic adds a fresh take on them and the game’s style just puts a smile on your face.