Let's start off by saying if you're not familiar with Detective Conan then you're wasting your time here, this spin-off is a parody of that series and has nothing else to offer.
If you're familiar with the series however, even if you only watched the classic episodes and nowhere near caught up with it, you can still watch and enjoy this show.
Hannin no Hanzawa-San is a simple comedy/parody with short 5 minutes episodes, a catchy opening and a beautiful ending song. Is it funny? It probably won't make you laugh your ass off (though it did get a few chuckles out of me), but it is very entertaining nonetheless.
If you haven't noticed by now from the title and cover, this show is about the shadowy figure that represents the culprits in Detective Conan, it's presented as a character named Hanzawa, so you already know what to expect from the kind of humor this show has to offer, but one thing I personally wasn't prepared for and found to be a pleasant surprise, is how the main cast from the original series are portrayed in this one.
Hanzawa-san portrays the world of Detective Conan in a silly way, as an (almost) apocalyptic city full of murder, which is hilarious by itself, but instead of doing that as a one time joke they actually build upon it, making it some sort of sarcastic world building, and it works well.
And then there's the main cast, who are not used as characters with roles in the story, but instead as the punchlines of their own parodies, for example in one episode Hanzawa shows murderous intent, suddenly Conan and Heiji start following him out of nowhere, they don't interfere with what's going on at the time, they're only part of the background and never even say a single word throughout the episode, they're almost creepy in a funny way, makes you feel like they're watching you all the time in this world, it's a subtle joke parodying how Conan and Heiji often tend to randomly look at a person and find them suspicious for no reason, and they're always at the right place and right time for a murder case.
The visuals are surprisingly good, the characters may look a bit different due to the art-style, but you'll get used to it in no time, especially if you never skip the opening song (which is simply fantastic).
There's really no reason not to watch this show if you're sold on it already and can find its episodes, it's very light and easy to watch without worrying about time, either way I hope you got something out of this review.
As of the time of writing this review, there are 6 episodes out of Hannin no Hanzawa-san and it's not clear how long the show is going to be (maybe 12 episodes, maybe more? Who knows?), and based on what we've seen so far I rate it 8/10, though that may change depending on how it goes in the future.
Your feedback will be appreciated, have a good day.
The used images are screenshots from the show.