I'm a big fan of these destinations. I mean, Japan in particular is an extremely popular travel destination, and I don't think I've ever heard anyone say they had a bad time there. Like u/throwawaygremlins said, though, it depends entirely on your interests and time of year. Would I go to Tokyo in July? Absolutely not. Japan and South Korea also have the potential to be pretty intimidating destinations if you're a first-time or relatively inexperienced traveller, especially off the beaten path. I found people to be polite and helpful most of the time, but I definitely felt the shock of being in a place where I did not know the language and the cities are so densely populated compared to what I'm used to. Some people love that new/semi-uncomfortable feeling, some people don't.

I think any location can be great for a honeymoon if you've done your research and it matches your interests and comfort levels. What are you interested in?