There are two David Lynches: there's David Lynch, a filmmaker with a diverse career that encompasses sci-fi epics, abstract horror films, and g-rated character studies, and there's "David Lynch", the weirdo who exclusively makes disturbing movies that operate on dream logic. When David Lynch's name comes up in conversation, people are mostly referring to the second Lynch, because he's the one that's easier to pigeonhole. The same way that "Kafkaesuqe" has come to denote a certain type of dark absurdism, "Lynchian" has come to refer to a certain type of surreal menace, particularly when it involves subverting suburban normalcy by juxtaposing it with unrestrained savagery - although almost half of his films have nothing to do with that.
I have to say: I've fallen into that trap, too. I have such a strongly negative opinion of "David Lynch" that when I think about David Lynch I often have to remind myself that I like the majority of his films that I've seem. The trouble is that while say, The Elephant Man is incredibly touching, a really well made movie just doesn't stick in your craw quite the same way that an incredibly frustrating one will, so I have to force myself to remember the Elephant Man while something like Mulholland Drive is always there ready at my fingertips.
The plot is not really the point in Mulholland Drive, but I'll give it a go anyway: a woman who might be named Rita is nearly shot by her limo driver but she is saved at the last second when another car hits the limo from behind. She escapes, spends the night sleeping in some bushes, then sneaks into a nearby apartment right as the apartment's occupant is getting in a cab to go on vacation. Later that day, the vacationer's niece shows up, since she was going to house sit while she was in L.A. trying to land a part in a movie. Meanwhile, the movie's director is being pressured by some shady men in a weird control room to cast a specific actress in the lead role, and when he refuses, they threaten him, freeze his bank accounts, and ultimately make him reckon with "The Cowboy", a weirdo in a Stetson who mixes vaguely threatening statements with upbeat aphorisms about politeness. Eventually the two women will sleep together - that is, unless they are secretly the same woman, which they might be - and one of them will eventually be cast in the movie (unless she's actually a fever dream and the movie never existed.)
So is this film a puzzlebox about a woman who might be real, who might be a hallucination, who might be an alternate version of another character, or who might a personification of Hollywood's ability to crush the innocence out of a dreamer? Or is it just a messy film built around amnesia, one of the most tired plots in Hollywood's script book? Is it about the nature of fantasy versus reality, an exploration of Los Angeles' dark heart, a dark parable about the risks of escapsim.... Or is it a half-assed rehash of soap opera plots enacted by a blonde, a brunette and a guy whose defining characteristic is that he always dresses like he was an extra in a seventy year old Roy Rogers movie? It's your call.
Most of the time ambiguities don't bother me, but I do want them to be intentional ambiguities. For example, the "but wait, does the top fall or not?!" ending of Inception never bothered me, because it was clearly meant to tell the audience something, even if the exact nature of it's meaning was debateable. Unfortunately, I often get the feeling that Lynch has a vague sense that his ideas hang together tonally without having any specific reason for why any of it works together. (This was Roger Ebert's big problem with Lynch, too.) Some of the identity switches and backtracks in this movie are clearly part of a bigger narrative, but I think some of them are red herrings that are meant to throw viewers down erroneous rabbitholes. I doubt the whole thing was meant to make logical sense - it was probably meant to make dream-logic sense, where an emotional tone unites everything even if all the ends don't directly line up.
However, there is a big difference between Mulholland Drive and Lynch's other dream-logic films: even if you don't want to take a deep dive into the (possibly shallow waters) of Wild At Heart, there's interesting stuff happening on the surface. (If you haven't seen it, there are voodoo priests, spree killers and Willem Dafoe with weird-ass baby teeth in that movie.) In contrast, Mulholland Drive's appeal is almost exclusively metaphorical - the surface storyline is dominated by an amnesia mystery that's pretty unfulfilling on it's own. That means that if you aren't going to watch it with an eye to decoding it, you're shit out of luck. Unfortunately, by the time that Mulholland Drive starts to really get meta in the third act, I had almost completely checked out, because I had long since given up hope on any part of this movie adding up to something real.
That said, you shouldn't necessarily take my word for it. While some people hear a Bob Dylan song and think "this cryptic work of art that would reveal the universe to me if only I could decode it!", I hear it and think "this pretentious piece of junk is hiding how empty it is under layers and layers of purposelessly obscure references!" In reality, both Mulholland Drive and that prototypical Dylan song are quantum works of art, functioning as both a particle and a wave at the same time - simultaneously epic and empty, depending on who is observing them. I can't guess what you might think of this movie, but I do know that when I watch it, I only see a particle - one slow, obtuse and empty particle.
Winner: The Cat