I'm currently at the end of Anachronox. This is my first playthrough, and my god, it's an extremely good 3D Adventure/RPG by Tom Hall. Made with the Quake2 engine, it is still one of the most stunning, epic and hilarious gaming experiences I've encountered. It mixes two genres much, much better than King's Quest did, with few random RPG elements and a strong focus on quests, puzzles and exploration. If you have a thirst for it, like I did about a month ago, it's just your thing

And it is only 6 bucks on GOG.
You might also give Simon the Sorcerer 3D a chance. While there is nothing attractive about its visuals, the writing is on par with Anachronox, and the 3D world is open for exploration (not as detailed, of course). And puzzle-wise it's a solid adventure game, just like the previous chapters. Only longer and better)