Codename: Iceman was a tough one. So was The Colonel's Bequest and Manhunter. I have not played Gabriel though and I think the people who answered QFG2 haven't played some of these others.

For what it's worth, here are some (mostly) PC games I've enjoyed in addition to the QFG games... - Dink Smallwood - http://www.rtsoft.com/dink/ - I'm frankly surprised it's not been mentioned on here yet... not so much RPG but a good short adventure with fun humor. Free download. - Peasant's Quest ...