Grim Fandango! I never got to the end, but I'm a sloppy gamer at best. The visuals and dialogue were amazing.

There is a team working on a real-time version of RIVEN, the sequel to Myst. They are pretty far along from the demos I've seen. It's remarkable work. This was work Cyan did not want to undertake, but some crazy fans who somehow have the time and funding to do this. Not sure how many people would want to replay it, but RIVEN holds a special place in my heart. I spent a lot of time there (that one I DID finish).