Far Cry 3. Far Cry 1 is fun, but its a straight shooter you can finish quickly. Far Cry 2 is a great sandbox... But have some annoying aspect such as a story that "reset" your progress at one point, basically asking you to replay the game twice. Far Cry 4 looks better than Far Cry 3 and have plenty of improvements but the setting and story are inferior.

And everyone should play Blood Dragon. No exceptions.