Yes, Flash Gordon is campy, and chessy, and trashy...it may be a lot of things, but most importantly, it is fun.
You have to take in consideration what the movie tries to be: a homage of the original 1930's comic strips. And while I haven't read them, I totally get the vibe and I know it succeeds wonderfully.
Knowing that, I can't really criticize the cardboard characters, the stupid premise, the hilarious effects..because that's the only approach a movie like this should have. Flash Gordon is the most innocent and likable hero ever, and an unrecognizable Max von Sydow gives a terrific performance as Ming the Merciless; everyone else is pretty much terrible, but they were having fun, and that's what it matters to me.
I have to also praise the soundtrack, made by no other but Queen. Can you think of a more appropiate band for a job like this? Queen itself it's campy and self-aware, that's why their music fits so perfectly with the film. Flash theme is even more memorable than most of their songs from the 80's and 90's.
I have to admit that the movie don't always overcome it's silliness and that the pacing suffers a lot throught, those being my only real complaints.
Flash Gordon is far from being perfect, but it has a lot of heart, and I can't help but love it.