For starters, let me tell you that I might be a bit biased, as this game brings back great old memories for me. I was a hardcore adventure fan, although I don't have as much free time anymore.
If you liked the above 2, you should really give Sanitarium a go. Sanitarium's story is constantly evolving as you play, in this respect it is similar to Grim Fandango, being split to multiple "acts", but its horror/thriller atmosphere is very different, you won't find as many jokes here, and you won't be laughing too much.
The puzzles are usually not too hard to solve and there are few easy action sequences, where you can't die, so you can mostly just sit back and enjoy as the story unfolds.
There are occasional annoyances while playing, most of them related to the controls, which many people don't like. Sometimes it's very easy to accidentally take the wrong staircase, making the character go up/down in an unstoppable animation. But this minor thing aside, if you like psychological horror/thriller dark themed stories, you should really try it. Along with Noctropolis, it was one of the few adventure games at the time with unusual setting. It's one of my dearest adventure gaming moments as I (along with the main character) have finally figured out what is going on, and the pieces finally fit together at the end.
Make sure you like the atmosphere before buying though, as it's not your usual goofy LucasArts adventure. There is a demo you can try, although it's very short and hasn't received GOG's compatibility treatment, might be hard to run on modern systems.

Let me put it this way: I can count every "traditional" adventure game I've ever played on one hand and I think this game is awesome. The story is cleverly told, the environments are unique and very engrossing, and, for the most part, the game has no mind numbingly obtuse puzzles/obstacles. The one thing I would point out though is that the navigation and movement in this game are kinda crappy. You have to hold the right mouse button to move which most of the time isnt so bad but when you are forced to do a lot of backtracking it can get kind of exhausting. If you dont think that will be much of a problem then I would say get it because it really has no other major flaws that would discourage a "casual" adventure fan like you or me, especially now that the price is reduced for the holiday sale.

Hm, I have been browsing these forums and it seems like the game has some nasty bugs with Vista/Windows 7. I think I may hold off for now...
Boo.