Seasons of the Sakura was one of the ones I've played. I saw all the endings in that one.
As for Clannad, that was originally a PC game before it got remade into a manga/anime. It's a romance-themed visual novel. Which is basically what most h-games are (not all h-games are visual novels though). Except h-games have X-rated content. I would imagine that the game is actually better than the manga/anime but I haven't sampled any Clannad at all yet so can't say. I remember watching the Tsukihime (another "high-brow" h-game romance visual novel) anime after playing the game and while it was enjoyable, the game was so much better (however the game did have a lot of filler. It probably took me 50 hours to get all the endings. And that 50 hours is pure reading.)