Oops, sorry. Was trying to edit an update my post from above, but I accidentally created a new one. If a mod see's this could you please delete this message.
Without stating the obvious classics that have been mentioned already, more recent ones I can recommend are: Machinarium Deponia Series (Deponia, Chaos on Deponia, Goodbye Deponia)
While Phantasmagoria definitely wasn't quality, I had fun with it. It's short, corny and very 90's. It made me want to play through Harvester again. I haven't played the second one, but from what I read there's not a lot of playability.
Tie between Zak McKracken and the Alien Mindbenders for the C64 and Are You Afraid of the Dark? The Tale of Orpheo's Curse for MS-DOS. I really wanted to like Broken Sword: The Sleeping Dragon for Windows, but I abandoned it half way through out of frustration. Maybe the XBOX/PS2 versions were better.
