Here's a version of a piece in just intonation—
https://www.youtube.com/watch?v=0i68ifRkitA
—and "modern" equal temperament:
https://www.youtube.com/watch?v=HEbi-7tPaqo
As much as people describe just intonation as pure, etc, at least in this example it just sounds wrong to me.
As far as I understand, just intonation requires instruments to be tuned differently for different keys and stops "working" if a piece strays from the key (which music from Bach's time will often do).
Equal temperament is our workaround for the physics which doesn't quite match the 12-tone system.