You're seeing a lot of hate because you're looking on Reddit for it. I cannot express to you how much of an outlier that kind of behavior is, except for maybe on Twitter where people who see it here, think it's okay, and then take it upon themselves to find other fans (or worse, the creators) and harass them.

It's just that this place attracts a particular kind of fan. When it comes to people bemoaning the manga and the second season as the worst thing in the world....you have to take it with a grain of salt. If you're looking at it when it comes to the anime, lot of people didn't like the second season, a lot of people did like the second season, a lot of people were like "yeah it was a season." The manga is about the same, but I'd say with more people liking it a lot while there is an EXTREMELY vocal minority who say it's awful. Most people have a mixed bag of what they prefer from the manga or the webcomic. Regardless of how they feel about story, pretty much everyone agrees that Murata is an incredible artist and one of the best currently working, and that ONE has a super-unique way of writing stories*** that transforms everything he touches for the better.

OPM is great. It's weird and funny and gorgeous; its treatment of characters and story can be insightful, hilarious, and a massive fuckin' gut punch in one blow; and we're getting into some HUGE fuckin shit both in the manga and the webcomic, One of the best parts about it is that, because there are three different iterations out there (webcomic, manga, and anime), you get not two cakes but THREE to choose from depending on your preferences--and then nearly an ongoing decade of fan content (art, fic, meta, cosplay, etc.) to look through after that if you're still looking for more to chew on.

***(Because someone is going to try to tell you otherwise since they aren't a fan of the manga--ONE is the only writer of the manga, while Murata is the artist. They collaborate on story beats but ONE has final say in everything that happens, and going by the way that Murata comments on things occasionally, I think he's also the only one who knows who it's going to end. The redraws we see are because the manga deeply elaborates on everything included in the webcomic [as ONE was hoping to do when he started working with Murata]. Because the story is more complex, though, certain plot points don't translate directly over from the webcomic to the manga, and as the years go on they need to be revised to fit smoothly into the broader story before they're finalized in the physical published volumes, which cannot be changed after the fact. The redraws exist because ONE and Murata would like to avoid actual retcons in the future. Technically nothing that happens is guaranteed canon until it's down in the physical copy, but it's treated as such unless it's announced that they're going to be revising certain parts of the story. The process of editing can last anywhere from weeks to a year. They can do that because Murata either worked out a deal with Tonari no Young Jump where OPM is published OR he helped create it [i can't remember], where he and ONE dictate their own schedule for releasing chapters for free online that they can change as they see fit up until the physical publishing of the volumes, which you need to pay for. Those physical volumes are many many many MANY chapters behind what's available for free to read, so there's a lot of headway for them to see how the story has panned out before setting the past down in stone and fans don't have to pay in order to enjoy the story.)