Sam Morrison’s review published on Letterboxd:
Before Robert Downey Jr became one of the most recognized superheroes of all time and before Val Kilmer was completely forgotten about, they made a little cult classic called Kiss Kiss Bang Bang, and it was/is awesome.
Nobody can really be described as redeemable in this film, but that's the pure nature of Los Angeles. Selling the seedy underbelly as a normal feature but fighting against it all the same, in hopes for the ideal life.
There's a fair amount of homophobia going on, which ties into Downey Jr's less than redeeming qualities. Kilmer plays said character, but also doesn't treat his unexpected partner with friendliness in the slightest. Though that does tend to bring out the best parts of the humor.
Michelle Monoghan is the perfect match for that girl who you "just have to have" and makes a believable case of being Downey Jr's childhood friend. They're just so back and forth all the time that you lose a little interest in if they really want each other or not.
With punchlines that'll tickle your funny bone in places you never imagined, mixed with a storyline that'll wrap you around its finger, and even some more tragic moments to reign in heavy drama, this genre blend is ingeniously devised. The only fixes I would have gone with would be more normalization for Kilmer's gay character and perhaps a few more jokes to leave less space between the great ones we get.