>>9669476Quite a bit, actually.
Nanos are slightly bigger and rounder, and take two LR44s instead of a single CR2032. The Nano also has a larger resolution screen (30x24 vs. the Mini's 16x16).
More importantly, the Nanos have games, additional animations, and more complex care mechanics. The Kamen Rider one has over 40 possible characters you can raise based on how well you care for it, how many times you fight off shock soldiers, and how many times the games are won.
>>9669050You can also go for the classic Nano V1 and V2 (both of which are just plain Tamagotchi characters) or the Pac-Man Tamagotchi, which has you raise Tamagotchi characters but there's a Pac-Man theme to the food and games.