Actually the sound quality is good. Its not particularly loud but it is clean and distortion free, I could distinctly hear multiple layers of audio in the soundtrack. I have spent about 5min just then just getting out into the the game world in Zelda and stuffed about the front of the cave you emerge from. Climbed some trees, rocks etc and just ran around in the grass. The speakers are capable of nice audio, the shuffles of running through the grass while birds and other ambient sounds played out was very distinct, I would say the audio is actually very good.
It of course does not sound as full as nice headphones or having a sound system capable of producing full bodied sound with authority, but the Switch speakers are definitely nice and clean with good detail.