I'm more on the edge on this, because I prefer to create my own characters, and I don't adopt that much. I do own a few CS myself, but overall, I have mixed feelings about CS in general. Half of them are to me either cute or have interesting concepts, while the other half is a mixed bag of interesting or bland designs/concepts and good/poor executions. I only like/am interested in quite a few popular ones. I'll also have to say the same with Open Species, because imo they're also a mixed bag of interesting or bland designs/concepts with either good or poor execution.
Now, back onto the CS part, I feel like most CS owners tend to be rather overprotective about their own creations, hence the name "Closed Species" meaning that you can't create your own without permission. However, offbrands exist, and they're everywhere, with most offbrand adopts only made to go against the concept of CS. Also ngl I actually don't like offbrands since I feel like it disrespects the CS owners and their wishes. I've also discussed offbrands on my own thread nearly a year ago, with the majority saying that they're neutral with them. While I agree that most CS look unoriginal in terms of designs, I think to me, what matters is concept execution. If a species concept looks great, but the execution is poor, then the species may end up flopping into obscurity, but that's just me.
Overall, I'm not saying that CS are bad in general, but I actually like and am interested in a few of them! I just can't seem to click well with most species.
Edit: Oh yeah I forgot that I posted here in the past, but I'm glad that I (Kind of?) changed my thoughts about CS over a year later.