Some of the episodes are just not interesting, but the worst ones for me are the ones that only looks good on paper and show but won't really work in real life. For example, the mist goblin legend murder probably won't work since the house is made of wood and definitely have some type of holes and small cracks. I doubt you can fill the entire room with water without water leaking. Also, it just takes too long and too risky. Another example is the photo mail from the clown since the culprit placed a doll clown in the room and switched it with the victim who was placed outside in the cold. What if the part timer noticed that the death clown was a doll in the house and the actual dead person is outside? Also, what if the the about to be married couple came close to the doll? Just too risky and easy to be exposed. Some I think are beyond ordinary people's idea like lawyer Eri Kisaki's testimony. I think even if the physics does work, there are still chances of it not being successful. Science is not always perfect when you actually do it.
Some bad episodes are the bad excuses the culprit has for doing the murder. The one with the hanger was ridiculous for disappearing weapon search case. In trick vs. magic, the murder did not even give the reason for committing the crime. The murder simply said he didn't regret it but made weird insane facial expression when he covers one side of his face with his hand. Beckoning cat from right to left is another one with really bad reason. The victim lend money to the culprit so he can have a chance to own his business and make his dream come true. Since he wasn't able to pay back, it is his problem for not be able to keep up the business well. If the victim never lend the money, he wouldn't even have a chance to open the business. The mountain witch's cutlery also has a bad reason too. This is because it should be the culprits fault for giving all the money he earned to his parents, who are gullible and naive. Sounds pretty ridiculous that the parents used the money he earned to go for risky stocks without even telling him. Besides if he really hate his job, he should just another job and repay his parents debt.
Anyway, there is just too many to name. But since there are so many murder cases, I can understand why it is hard to make up excuses for killing people. Overall detective conan is still a great show.