Thanks for recommending the liver thing, Gabe. I'll try it.
My favorite amateur adventure game so far is Nelly Cootalot. Very Monkey Island like, but stands on its own. And can be really funny. Rather great puzzles too.
Mental Repairs Inc. that I mentioned before is another worthy title and technically it's as good as many current commercial adventure games. Oh, and it's heavily LucasArts inspired as well. Most amateur adventure games are.
I wrote a short review
for it if someone would like to know more.