
It's not that this movie is particularly bad. The acting is fine. Some of the comedy works and, to agree with some of the people at the link above, the movie does have some very quotable lines. It's just that the plot is so ridiculous. I'm sure it was meant to be over the top and just a bit of fun to showcase the band and the music but it goes too far into extreme silliness.
To get away with this kind of silliness you have to start with a premise that is credible. This movie has a very culturally important sacrificial ring stuck on Ringo's (of course) finger. In the real world you'd just explain the situation to the famous drummer and I'm sure he'd be obliging (might even pay for his own tub of butter to help remove the ring).
However, for some reason, the ring has to recovered covertly by its obscure, Asian Cult owners and from there stupidity ensues. Complicated further by some mad scientist type who believes this ring could help him 'rule the world' (why I don't know? It's a symbolic ring with no real power or significance to anyone other than it's owners).
Maybe I missed something along the way but finally, after 'Paul's tiny adventure on the floor' I decided enough was enough and switched it off. Even as a showcase for The Beatles superb music, there just wasn't enough of it to keep me hooked.
All I can say is that you have to be a real Beatles fan to endure the entire movie. Clearly this was made at a time when the band could release virtually anything and it would find an audience to make it all worthwhile.
Personally this movie probably needs to be remembered for its highlights because as a whole, for me at least, it is unwatchable.