It's one of those The Art of Creating Art films that I'm partial towards, though I must add that I have not sat down to watch this film in a number of years, so it may not have aged well, but I remember digging it immensely...

And you also should not only check out The 400 Blows, but also the entire Antoine Doinel series... Criterion released an excellent box set which collected all 5 Doinel films... and also peep Jules et Jim and Shoot the Piano Player if you can... all of those flicks are Truffaut's best, imo...

As far as Godard, I'd also check out Alphaville and Masculin-Feminin...
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