It is more than faint praise to say that Popeye is far, far better than it might have been, considering the treacherous challenge it presented. But avoiding disaster is not necessarily the same as success.
I think that the power and the theme of the film lie in the fact that while some characters are more "major" than others, they are all subordinated to the music itself. It's like a river, running through the film, running through their life.
I am not sure that any indispensable statement about opera has been made here, and purists will no doubt recoil by the irreverence of some of the images. But the film is fun almost as a satire of itself.