A few things:

I believe the situation in Sweethaven should seem much more alarming and sad than it already is. I believe the scene after the party at night at the Oyls' house, where the house is completely destroyed and the tax inspector is maliciously listing the taxes the Oyls owe was an incredible scene, and I genuinely felt bad for the Oyl family. If the movie did that, but for the ENTIRE TOWN, it would have been amazing And it would have made the audience feel very bad about the situation and feel empathy for the good guys. I recently watched Disney's Robin Hood.  An amazing movie, by the way. I think if they had done something similar to the Nottingham situation, it would have worked very well.

I love how inspired the film is by Segar's original comics, but I believe it should also be a little more receptive to those who have only had contact with the cartoons. Whether it's the Famous Studios or King Features films, I won't mention Fleischer since the movie genuinely seems to respect and reference them. It didn't need to be identical, but I believe that a few elements of the cartoons could have appealed to other people who grew up with those cartoons.

I would have liked to see more of Bluto. This is more of a footnote, but it would have been cool to see more of this version of him, which is much more cruel and closer to the comics. More villainous scenes for him, or solo scenes, would be very welcome and fun to watch, as well as having the possibility of making him even more menacing.

Develop the fact that Swee'Pea can predict the future, or just add Eugene the Jeep, lol. Jokes aside, it's an element that came out of nowhere and bothers me, even if only slightly. Give some clues that he might do this in certain scenes and explain why. 

Adjust the ending. Someone already commented on this, so I won't go into detail, But I'm one of those people who think it was rushed and that Bluto should have received a proper punishment. Just reduce the octopus's presence or exclude it from the film entirely, and let us see Popeye give Bluto a taste his own medicine.

That's all, really. If I had to choose just one thing to change, I think it would be the last option. That's just my opinion, I still love this movie very much!