Was he really GOING for “40s style” dialogue? I mean I always got sort of a 1930s-1940s vibe from the OT (since it was inspired by Flash Gordon and all), including the delivery of the dialogue, but was it (the dialogue) really INTENDED to give off that vibe? I just thought it was a result of his self-admitted inability to write good dialogue.

That might be why fans forgive the OT for its cheesy dialogue delivery, but chastise the prequels for it - the rest of the OT (the original versions at least) has an old-timey feel to it in general due to its drawing from early-20th-Century film, so the dialogue fits right in with that aesthetic. The prequels, on the other hand, have a distinctly modern (by late 90s-early 2000s standards) look sound and feel to them, right down to the digital cameras they were shot on, so the bad dialogue/acting sticks out more.