It's been 3 decades already. I loved watching Detective Conan as a child but it has far overstayed it's welcome than One Piece. I bet this is gonna go on for much longer considering it's became a staple and movies are the highest grossing in Japan.
The art style has turned for the worse, murders don't look brutal and horrific as they did in the beginning. It doesn't have the same horror and thrill that it had in the beginning. Also those pointy fucking noses suck. The character moved their face a bit? I need to draw the pointiest fucking nose that is far from mouth as possible. He just won't drawing them, don't even get me started on Ran's "horn". I'm sure he's aware but why keep drawing it this way?
The mystery of the Black Organization worked great initially, Shinichi was reckless in pursuing them, almost got caught several time but overtime has gain too much of an upper hand. All the good guy organizations such as FBI are helpless, they need him. BO has also lost it's charm with too many spies from the members we know of (including non-canon material). They still get away with all the crimes that happen so they're competent. I wish there was more than subtle showcase of their ability.
Don't get me wrong, Gosho is genius at creating these crime scenes and conflicts between them but BO content is very less. The plot also moves at a glacial pace, with only 233 chapters being focused on BO out of 1145 chapters so far. There's also the floating timeline, now that the series is in line with modern world BO should've been exposed to public at least. Rum was revealed over more than 15 years ago and we finally got to know their identity. Wonder how long it will take to "catch" him. And if the BO boss if that ever happens.
One downside to writing these amazing crime tricks is you need to be a genius at solving them. Shinichi has to be the one solving most of them. Kogoro while he got some development, is still useless most of the time, doesn't question how he solves crime while "sleeping". No one questions Shinichi being behind him talking. I get it's a plot convenience but you just can't unsee it. Now that we can't have only a single genius, we get others. Guess what they're slowly revealed to be connected to each other. Shinichi is a walking encyclopedia at this moment. Fans can't even try a hand at solving these crimes because you must know either Japanese or insert country general knowledge. Yes those kids are annoying and suck, especially Ayumi who gets caught way too much (especially in anime filler). Ran also needs to be more self-aware considering how much crime they encounter.
Gosho likes writing Romance especially childhood friends, so if you're fed up of childhood friends losing in popular romcoms you'll be a bit happy here. Couples before getting together is the best part of these ships. You just can't help but root for them but Gosho sucks at writing them after they get together. I very much understand why people think Shinichi x Ran is toxic and if I were Sonoko I'd be telling to leave him too (although it hasn't been long in-universe it feels far more longer considering the chapters). Conan x Ai feels more appealing than Shin x Ran.