I don't get it

I love Clue and Murder by Death, but I don't get this movie.

I kept waiting for something humorous to happen or a joke to make me laugh, all I got was 'weird moments' or 'surreal boredom', and 'disgusting repulsion'.

I never expected Nurse Ratched and Columbo to sing a duet, but I never knew how horrible that would be, either.

Maybe I am too tired, I just couldn't finish it, it just seemed to plod along bringing a boring non-joke after another, and occasionally break into song or some sort of weird musical.

What happened here? Where's Peter Sellers' Asian Stereotype, Lionel Twain's hilarious anger towards that stereotype, and all the unexpected things in a mysterious mansion?

Maybe this is a parody of Casablanca or something, but I just don't get it. Is this supposed to be humorous or funny? Does anyone laugh just because someone keeps drinks in a drawer?

Falk is a genius, but I don't know what the heck he's trying to portray here. No one as likable as Columbo, no one as funny as Diamond, so I don't know what to think or feel here.

Is 'get off his back' supposed to be funny? The jokes seem forced and completely humorless, so all the viewer gets is plodding boredom.

I also can't really see that evil nurse as any kind of feminine or romantic character, so there's that. All I see is a demon every time her ugly mug is on the screen, and her evil voice scratches my mind until I can listen no more.

Something went terribly wrong here, I just wish I could figure out what and why. I'll go back to Murder by Death now to wash this awfulness off my contanimated soul.