My problem is deciding which games not to include. I'd like to list all the old LucasArts adventures, but that would take up too many slots. I hate leaving out The Dig, with its wonderful soundtrack, the one of a kind Loom, and Day of the Tentacle, probably the funniest game I've ever played. So I decide by using criteria like "TLJ, Riven, and Syberia don't need my help because several other people are sure to recommend them."
I also wanted to list a variety -- humorous and not, puzzle-oriented and not, and most importantly, new as well as older games. Generally I only listed one member of a series, though you can see I have 2 or 3 exceptions. (I assume someone who enjoyed GK1 would seek out the other two GK games. But I know of people who enjoyed Zork GI but not Zork Nemesis and vice versa...)
Here are the older (pre year 2000) games I'd recommend (minus those I didn't have room for)
Secret of Monkey Island
Curse of Monkey Island
Gabriel Knight 1
Myst III: Exile
Zork Grand Inquisitor
And below are the newer ones:
The Egyptian Prophecy
Return to Mysterious Island
Sometimes I wonder if we shouldn't have a separate list of games that are generally easy to get running on newer computers without needing DOSBox or fussing with compatibility mode, etc. But Microsoft's patches have made this difficult to predict even with relatively recent games, what with needing to run them as administrator and such. The LucasArts games may actually be easier to get running than some of the new games now, thanks to ScummVM. And GK1 and GK2 now have the fan-made XP installers.