As a person who has played the beta version of the game, I can say for sure that it is not a clone of RLE.
Oni's game is one big sandbox, where you are thrown in and given the opportunity to do anything without any plot. You maximize the stats of girls, change their personalities as you want and... wait for the next girl to come out?
In the case of THN, you take part in the story of your character and his newfound powers. Personally, I liked what I saw in terms of the plot, and I was pleasantly surprised by how the writers handled some of the characters that I didn't find very interesting before the beta.
I won't compare the art, it's a matter of preference.
As for the technical state, I can say for sure that the game does not freeze as it happens in the case of RLE, when you have to wait for someone's third-party mod to fix the performance. (A note for all the jokers: I play BG3 on high graphics settings and don't experience any problems).
We beta testers are just as excited for the release as you are, and we can only hope that we were able to find all possible bugs in the time we had.
If you have any questions, feel free to ask.