Full disclosure: I'm not a Patlabor fan at all, but I own and really like this movie. I've watched it at different times in my life, with years between viewings, and each time I've liked it more. Now, watching it again at a much more mature age, I fully enjoy it. It's not at all an anime film that kids or teens (or adults wanting to shut their brain off) would would watch to enjoy, and although I don't even enjoy police procedurals like I, ironically, did as a child, I feel this mature story is very underrated. Furthermore, now that I better understand a few things about film, my enjoyment was enhanced, especially regarding shots, editing choices, and themes in particular. Anime tends to bash you over the head with themes, even directly telling you over and over what they are (Gundam Wing, for example, is really bad about this-though I really like it), but, while the themes are clear, this film doesn't do that. It's another reason why it seems to be geared towards mature adults (not implying you're immature if you don't like it). It reminds me of Ghost in the Shell that way, except the action in GITS can draw all ages-but strip that away or minimize it even more and you have a very adult investigation story that would bore people who don't like such things.
I've tried to get into the Patlabor series, but it's always come across as a boring, childish A. D. Police or any other mechanized police unit anime. I don't like the Labors or the uniforms or, really, the characters. But I was fine with how they were utilized in this film.
Also, something I especially like is that the characters in this movie actually look Japanese!! I love colorful characters, BUT if the characters in this film looked like Westerners with Japanese names, I wouldn't have been able to take it as seriously (plus, it would contradict one of the major themes). The point is that it looks and plays more like a live-action film than most anime, making it easier to focus on the subject matter, and I appreciate that.
I would say watch this if you don't mind a slow-burn (that doesn't drag) police procedural with a sprinkle of intrigue and horror.