I started with True Love '95. :) It was a decent game, but probably I liked it only because I've never played something like that before.
Good H-games are hard to find. The first good H-game I've played was Kana ~Little Sister~. But it's more like a novel with a very limited control over the story. The story itself is very dramatic and sad, imo. And has a low amount of sex. A good review:
http://forevergeek.com/articles/kana_little_sister.php
I downloaded School Days, because it is said, it's a very good game, but I haven't played it yet.
Critical Point was another game, that I liked more or less.
I played all the X-Change games and The Sagara Family too. They were sometimes amusing, but that's all.
There are a few more games that I've played, but can't remember now... :)
Btw, the same goes for H-animes. There wasn't even one that was close to being good, imo. No, not even Bible Black.
Almost forgot Inyouchuu. xD For some reason I like that H-anime, but plot wise it's still very bad(?). I'm playing the game now, but can't give You an opinion yet.