I just started replaying the Monkey Island games this week after about 15 years since I last played the original. Definitely one of the "best of breed". Sam & Max were enjoyable, as well as the Indiana Jones games, but Monkey Island was perfect in that it never took itself seriously so it didn't suffer from the "why the hell do I have to do this?" factor that some adventure games did.

In general, I think LucasArts was probably the best at this in the 90's.