I was expecting the normal isekai/fantasy trope of the MC being introduced to ugly or strange-looking girls for marriage, but dang:
She's cuter than his current fiancées. Just take her too dude, your father keeps telling you, polygamy is OK.
Now, concerning introducing other games, because reversi is an actual trope of the genre now...
Weeell, first, the setting is clearly medieval European-ish, so chess, checkers and probably a lot of card games would already be in circulation. I mean, he didn't just introduce entertainment to the world, just one game for all class and age.
With Reversi, it's also plausible that a 10yo noble would be capable of inventing it. Especially if checkers already exists.
Also, he wanted it to be available to the normal population, and I really doubt that a complicated game like go or shogi would become popular.
Now, what I would introduce is UNO. But reversi is a good choice too.