Like not caring about if his girl is in pain, making her do stuff she doesn't want to do during sex, facefucking her when she didn't want it, anal when she didn't want it, et cetera.
I assumed the engine was of less importance than the content. Most people don't find the specific engine a game was made with to have an impact on how much they enjoy the game. Not directly, at least.
Why Ren'py specifcally, by the way? If you want visual novels, you should specify that.