I need to catch up with EVERYTHING Truffaut I've only seen The 400 Blows.
TBH, outside of Shoot the Piano Player, and possibly Jules and Jim, I'm not overly fond of Truffaut's films. I can see why people like them, and they're good, but they just don't attract me.
From that era I think I prefer Antonioni's movies. One classic thing that Truffaut did that's worth its weight in gold IMO is his extensive interviews with A. Hitchcock-- available in book form, and a little on video. In those days it was rare to be able to get into the mind of master directors-- at least in the U.S.