The last adventure game I completed was The Shiva by Wadget Eye Games. I got it for free during their Yom Kippur special a few weeks ago.
While humorous adventure games are my favorite, I do enjoy the occasional serious adventure. And this was definitely a serious adventure I enjoyed. While it was a short game, it took me a while to get the good ending. There's one more ending that I want to try though. I really like it when adventure games have multiple endings, because they are so linear that you don't really want to replay them too soon after completing them otherwise.
Another thing I really liked about this game was that when you finished the game, there's DVD style extras. There's blooper audio files that come up when the game is completed on the good ending, and you can view the game with DVD style commentary if you want to.