Just completed The headmaster, and I have played Ecchi Sensei,I loved both and they were amazing in their own way, Headmaster has amazing animations and interactivity, Ecchi Sensei has great story, suggest something like this
That game fucked my head so hard... age of the girls never mentioned so its up to your interpretation. Great writing, really flashed out characters and at times really dark. also breaks the fourth wall quite frequently.
Following, because I LOVED the headmaster. played it almost obsessively until i finished it. I do not believe I have played anything better yet.I had high hopes for Ecchi sensei, but it bored me .. even with the patch, it was just way too slow to get to action, so I deleted it.
Personally, I have my own list, and I'd rate Headmaster and Sensei for top. So I can share other two. It should be Being a DIK ofc and the Harem Hotel.