The only thing I miss on GNU/Linux is a good alternative to CheatEngine, with popular game scripts from FearlessRevolution.org - creative use of such scripts can tremendously improve (single-player) gaming experience.

For example, I used to give a huge population boost to computer opponents in Rome: Total War, so they would be able to field big armies for me to crush. Without it they quickly depleted their manpower pool and after the initial clash the game turned into a tedious mopping.