It sure was lucky for Columbo that the murderer said "t'isn't," instead of catching himself and saying "If you say so" or something.
But we do have the surprise of Robert Vaughn getting killed and the "ah-ha" factor of the stencil message being revealed. ("He was going to marry the kid!")
The first time I saw LSTTC, its eccentricities drove me nuts, but now I have fun with it.
This is the only one of the original 45 I actually hate. The reasons have been discussed by others above. In a nutshell, though, it's just too quirky/eccentric for its own good. The finale is weak, and the whole episode feels like some snobby art-house film.