Disregarding all the usual "bad Chinese company is bad and unethical" stuff that somebody else will probably cover:
As a reader, as far as I know, the only reason to really dislike it is the pay-to-unlock system where you basically end up paying per chapter. But honestly, it's just a more micro version of locking chapters in bulk behind Patreon walls which far fewer people complain about. Though, some readers might be put off by the hundreds upon hundreds of "reviews" that are 5 stars with copy-pasted text that literally reads like "Fdshgghrfesdhhhhhhhhhhhhhhhhhhhhhhh." You can't really trust any numbers on there to be legitimate.
As an author, they are manipulative, unresponsive, and absolute utter shit. First off, if you post your stories to their platform and then want to delete them, there's no way to do it. If you email them and ask them to please remove your stories, they will lie to you in your face and say that they can't. That they literally can not delete the stories (despite somehow doing it whenever DMCA'ed). I had to upload gay porn to my cover and spam copyrighted material into my stories for 3 months in order to get Webnovel to finally realize I was breaking the rules and to delete my stories. Then there's all the controversy regarding their contract which is basically putting you into slave labor while taking complete ownership of your series away from you for less pay than you would make pursuing the normal Patreon -> Amazon route. Then there's not being able to use italicized/bolded/underlined text which is all extremely simple but not possible at all there, which is pretty silly. That being said, to try and be fair here, they have an excellent portal for authors with tons of stat tracking. Their author portal is honestly the best one out of all web serial platforms I know of.
So, it's alright for readers but shit for authors unless they're desperate, clueless, or just don't care about being taken advantage of.