Not for everyone, but come on, I have seen far worse that has been acclaimed as great films. It works better seeing both versions considering Warhol was interesting in replication (not to mention that he probably never took himself that seriously in his art anyway). I also felt hungry after viewing them one after each other...interpret that however you want, but if you do, you have a filthy mind.
In a sense it's pretty idiotic and juvenile, on the other hand it's pretty incredible how something can be so simple and calm and also confrontational to the audience.
I think people hate Mario Banana I because they didn't watch Mario Banana II, and that's necessary to really understand the deep motivations and the strong inner fight Mario suffers to eat a banana. More than that, the banana is a symbol so subtle of a penis that most people just can't get it, so they can't get involved in the edipic conflict of Mario, and instead of watching Mario actually thinking the banana is a penis, they just see Mario confusing a banana with a penis, missing the plot.