The only positive things I have to say about it are that the default music that plays is kind of nice (song #3) and that it doesn't crash. Even on "hard" mode, the AI as far as I can tell just picks a legal move at random. It doesn't even do a thing to protect the corners, it has NO aversion whatsoever from putting a piece down that is one vertical and one horizontal position away from a corner, and that's a GREAT way to give your opponent the corner because then all they have to do is get a piece of their own ANYWHERE along the whole diagonal without converting that piece that's 1 up and 1 to the side of the corner to their own color and then they can get it. There's not a LOT of strategy to even potentially program into something that plays competently and you didn't do it even so.
But there's also an issue with when it decides the game is over. I can see why you did what you did. The reviewers below are complaining that there is no "skip" option in reversi/othello, you are REQUIRED to move unless you have no legal move, but I can see why you did what you did - to save yourself the trouble of the program testing to see if there are no legal moves and skipping your turn automatically. And that's fine, I guess, it makes it into a variant of othello. EXCEPT you also implemented it bad in regards to how the game decides the game is over. It decides the game is over if both players skip a turn. Which means that even if you have a legal move and you choose to skip, if the computer then skips then it's game over. And that's stupid. It declared me as the loser even though I had a corner just because I played around with the "skip" feature and happened to have fewer pieces on the board at the time, even though I could continue playing, I had plenty of moves, and I was flagrantly going to win. ALSO, it doesn't end the game on the spot when I completely erase all presence of the computer's pieces on the whole board. So I had like 37 pieces on the board and the computer had ZERO, and it didn't decide I won the game unless I told it I wanted to skip and then the computer skipped. This is how I know the true purpose of the skip option. It was just a shortcut for you, rather than having the computer decide whether you had legal moves, just for the player to decide manually if the "skip" function was appropriate. And it could be more interesting if you did that, if you didn't have it end the blasted game if both players skip turns. Maybe do it kind of like in chess, if both players skip 3 times in a row then end it, but not just for once experimentally. It's an adequate game at best in any case. It's a stupid AI that can't play at all even in hard mode (which begs the question, what even is the difference between the skill levels - does it even do anything differently if you set it to medium or easy?), its extra feature doesn't work right because it ends the game prematurely if you use it, and that also relates to it requiring you to do something annoying to make it identify the game is over if it ends before all 64 positions are filled because neither side has a move. But hey, it's ok music at least. Frankly mitsuku's othello game is at least SEMI-competent even if I win it over 90% of the time, it's at least not moving completely at random, and it knows when the game is over and when the player can move so there's no need for a manual skip turn button.