It took me some getting used to but it's not bad IMO. It's more that its conventions are a bit different from the commercial readers but that's not a bad thing.
And recommendation caroussels are a bit too much like advertising to me. Something I wouldn't want on self-hosted stuff.
Koreader's OPDS implementation is VERY rough around the edges. It doesn't support much of the metadata and doesn't follow the spec very well. I had to write hacks in Kavita to give users better support for it. (My understanding is Koreader isn't too hot on OPDS in general).
Everyone here is lauding kobo for being so 'open' and 'hackable', but when I set mine up in 2022 it kind of just felt like they just weren't as good at fucking me over and subverting my intentions as Amazon. Kind of like being an intruder in your own home. Have things changed? Should I update my setup?