I'm talking games that had a real impact on your life, if any.
For me i would say my number one game of all time did me a great favour, and that game is:
Final Fantasy Tactics for the Playstation 1. The reason i say it did me a great favour is because of the age i started playing this masterpiece. Not online did the character Delita Hyral show me that its awesome to be a manipulative mastermind (Is he good? Is he a bad? *Gasp*), but the almost chess like gameplay got me thinking tactically about almost everything and breaking day to day problems into achieveable objectives, which has stayed with me to this day.
I rented it when it came out for N64 (I was still young), and combining the adult material, the depressing ending, and the (cute) visceral killings; really had an impact on me.
Best lesson learned: It's fun to go around drunk, pissing on things while hitting people with a frying pan.