The Clerks franchise, being the one that launched Kevin Smith's whole career off, is clearly his most personal and dearest to his heart out of all of his IP. Therefore it's no stretch to assume each Clerks entry is an amalgamation of what Smith himself is feeling or reflecting on in his personal life at the time of creating it.
And this time around, with Kevin Smith fresh off of a heart attack in his real life, it's no accident that themes of mortality heavily seep into every pore of this film. And what happens when we're smacked in the face with our own mortality? Much like the trope of our "life flashing before our eyes", it's very commonplace to look backwards into the past at good times and view them under a different, more appreciative lens.
This film is exactly that: the artist looking back at Clerks 1 (mostly 1, but a little bit of 2 as well) through that nostalgic lens. Smith's reflection on his own mortality bleed through to the characters flashing back on their lives in the same manner. Smith called this film his "Jersey version of Cinema Paradiso", but I saw it more as his version of Fellini's 8 1/2, especially given that he is literally holding a camera in the film.
The trilogy is now thematically complete: Clerks 1 embodied youth, part II aging, part III dying. While Clerks III may be an interesting enough art piece for these reasons, it's just nowhere near as funny as the other 2. To be fair, it's not really trying to be most of the time with the heavy themes it's taking on. But still, it is a Clerks film and a comedy, therefore it does have humorous lines and moments all throughout, even in the more morose moments. And these were simply nowhere near as funny as the other 2 Clerks films.
Overall this film did an excellent job on the nostalgia & fan service if Clerks means a lot to you personally, but otherwise it is the weakest entry in the series in terms of comedic substance.
