First iPod and iPad were fine.
The first iPad was ok only because it truly was "just a bigger iPhone". But they didn't really make features that were unique to the iPad and took advantage of its bigger screen for a few versions afterwards.
I would say the main function of an iPod OS is finding what you want to play, not actually playing it.
It was extremely easy if you tagged your mp3s properly.
The first iPad was similarly expensive, thick and underpowered. It wasn't until a couple generations in that it was good.