While it received mixed reviews for being a 3D fighting game rather than a traditional side-scroller, Castlevania Judgment features a stellar soundtrack and gorgeous character designs by Takehito Harada. It squeezes a full 3D fighter into a very small file size. 💥 Geometry Wars: Galaxies (~250MB)
For the modern enthusiast:
Retro Studios delivered a graphical masterpiece that looks like it should be 4GB. The game uses clever texture reuse and side-scrolling perspectives to keep the file size down while delivering a brutally difficult platforming challenge. It is a masterclass in optimization. wii games under 500mb