Thanks to everyone that recommended it.
It felt like a fun Raymond Chandler-inspired buddy cop movie. No surprise it was written by the Lethal Weapon dude. That also made it feel more like the type of fun crime movie that you'd see in the 80s, too. So it kind of feels like an 80s movie, yet it's inspired by old chandler stories, noirs, and pulp stories. Val Kilmer and Robert Downey Jr are both awesome in the movie, there's nudity, and lots of generally funny bits. The movie has a slightly dark sense of humor, which is always appreciated.
I mean, the movie isn't perfect; it's a bit to convenient in its plot developments, but that's not only a product of the old detective and noir influences, but also the neatness of buddy cop films. I don't understand why this movie wasn't given a high profile release. If it had been released 15 years ago, it would pretty much be a guaranteed huge hit. Not that the movie is dated or anything--the formula is just reminiscent of the era when a fun movie didn't have to do anything other than have fun, with no regard or focus on special effects, huge stars, gimmickry, awards pandering, envelope pushing. . .maybe that's why it wasn't pushed by the studio, and buried with basically a non-release. The movie is basically unambitious in every aspect aside from its cleverness, and the masses don't go to movies for good dialogue.
So, Kiss Kiss Bang Bang. It's good stuff. I bet that just about everyone can find something to like about this movie. Robert Downey? He's got it going on here. Val Kilmer? Easily, easily the best thing he's done since the 90s. Fun dialogue? In spades. As a matter of fact, the movie really has nothing to actively dislike, aside from the convenience.