Yeah the base $20/year subscription includes Cloud Saves, online multiplayer, a couple exclusive games with Tetris 99 and Pac-Man 99, along with NES games and SNES games. And the NSO smartphone app for voice chat The $50/year Expansion Pack is only for N64 games, Sega Genesis games, Animal Crossing paid DLC, MK8D paid DLC, and Splatoon 2 paid DLC.

Keep in mind though that not ALL games support cloud saves. Like all the Pokémon games and Animal Crossing: New Horizons don't for example. 

The base subscription also includes game trials. And everywhere but the US the (for me) #1 reason to subscribe, vouchers.

Oh that's right, game trials! Those are so few and far between though lol.

I remember hearing about vouchers, but since it's not available in the US, I don't remember what exactly vouchers were. Was it your choice of 2 games for a overall cheaper price?