OK, I finally got to see UTSL....and, first time through, I found it at least quite watchable. Going in I think one should know that it's a Pynchonesque shaggy-dog story with neo-noir inflections (including quite a bit of causal nudity) and a bit of a '90s retro vibe despite being set 'now'. If that doesn't *sound* at all like your cup of tea then UTSL probably won't be.
The Long Goodbye, Lebowski, Inherent Vice, Rear Window, and Lynch's Inland Empire are for me the obvious points of reference for UTSL. It's not as accomplished as any of those with the resolution of the main plot-line in UTSL being a particular problem: suddenly the film gets both lamely talky and visually insipid. It Follows laid a bit of an egg near its end too! Both films, however, pull things back for strong final scenes and shots so their endings aren't complete busts.
In sum, then, while I can't *strongly* recommend UTSL, I'd say it's a fair amount of fun, maybe a 6.5-7/10, for people who're prepared to run with its rambling nature and basic slightness.
Update: On the last 'slightness' point: I didn't get the sense that UTSL had anything to say about anything beyond 'here's all the pop culture I've ever consumed'. Something that might have given the film *some* depth: if the black hole of what Andrew Garfield's (barely named - I had to look it up, Sam) character used to do for a living was filled in. If he was supposed to be a failed screenwriter-style, Hollywood dreamer then certain lineages (back to Barton Fink, In a Lonely Place, Sunset Blvd, etc.) would be clearer and lots of the script's affectations including the trail of dead bodies never followed up would have as a definite possible interpretation that we're in a movie-long skid through a screenwriter's imagination. In that case, one thing the movie would be about is just capturing the mindset of being a down-and-out writer in hipster LA (hint: you fantasize about scoring or semi-scoring with one after another hot alterna-chick, while you wait for that last credit card to be cancelled).
It's a little irritating that UTSL never nails down *anything* enough even to make this 'Scriptnotes The Movie' interp. a fully determinate possibility.
BTW, I was a bit irked by IMDb (following official credits apparently) not listing a credit for 'Owl's Kiss'. Googling hard I was able to figure out she was played by Karen Nitsche, a French dancer and model based in LA. She has an IMDb entry but no credits (I didn't know that such a thing was possible). She has a vimeo page with this vid. of her dancing along to Chaka Khan's recent comeback record: