With so few good new titles being released these days, especially by major studios, I figured I'd make a thread for everyone to share your favourite classic or older games, especially if they're lesser-known titles that others might have missed at the time.
I'll open with The Saboteur (2009), Mercenaries (2005) and Saints Row 2 ( The 2008 original)
Thief 1+2 (you can play 3 as well). Also has tons of fan missions, which are fun to play.
Old school adventure games. Monkey Island, Indiana Jones, Loom, Quest for Glory, Simon the sorcerer, Discworld, King's Quest, Ween: The Prophecy, Gabriel Knight, ...
Definitely play Loom if you haven't.