This Side of Paradise is incredibly disjointed, as befits a novel that was evidently cobbled together from a number of originally unrelated stories and novel fragments. To say that this disjointed quality is what Fitzgerald intended would be giving him too much credit for planning ahead, but it sounds like it would be accurate to say that when he settled on this method he accepted disjointedness as the price he'd have to pay for it. And tried to make a virtue out of necessity, by playing up the disjointedness, shifting tone and format at will. Just goes to show that postmodernism is no such thing.
Is it effective? Well, I enjoyed parts of it a great deal. The out-of-nowhere intensity of the love affair in Maryland with Eleanor, recounted in the "Young Irony" chapter, is brilliantly moving, really capturing the insane romanticism of youth. There were other bits here and there that worked really well, too.
But they never did hang together well enough for me - the thing is I just don't believe that Fitzgerald's heart was in the disjointedness. If he was really a postmodernist at heart, if he really had meant to challenge traditional fictional notions of the unified personality, the format would have meant something and the novel would have worked, but I don't believe Fitzgerald believed it. And so the novel as a whole strikes me as glib. Beautiful and effective in parts, but not in other parts, and not in the whole.
The worst aspect of it was how he fakes his way through his protagonist's war experiences. As is well known, FSF spent his WWI Stateside; in his second novel he depicts this experience vividly, but in this book he seems to have felt that to speak for his generation (as he so clearly wants this hero to do) the hero had to have served in Europe. But because FSF himself didn't serve there he has nothing to say about his hero's time there. He glosses over it, but still expects us to believe the guy is seriously affected by it. He's conning us.