The chess level is good. Easy is really easy and the higher difficulty levels offer a decent challenge. It is a decent game of chess with a bonus. The scenes are not really interesting (for none of the opponents). Tentacles are really not my thing.
Some ideas:
My personal preference would be the opponent loses clothes instead of getting their clothes damaged (racypoker.com has a very straight forward strip chess game for example). The state of undress could also be affected by how much advantage you have over her? Instead of a checkmate you could first take all her pieces for an extra reward or something like that. Now, if you win, she instantly loses all clothing, and due to the pop ups, you can't eve see it. Also, she doen't move or have any additional poses.
What also could use improvement is that the girls are very passive (no emotions, really). If you choose for sex in the scenes (or as a forfeit for losing), you could make her appear to like it, or even make her cum (too), depending on what interactions you choose. You could even make it a challenge to outlast her.
Lastly, perhaps it would be cool that if you win she would need to do some kind of forfeit, and make this depend on how you won, or something like that.