Unless you are some strange Ritalin-popping, sugar-addicted 12 year old whose game library starts and ends with the Call of Duty and Halo titles, you should have at least heard of the Mass Effect series. Brought to life by the daddy of modern western RPGs, Bioware, the series is an action RPG space opera trilogy. If for some reason you have yet to play what is considered by many to be the ultimate sci-fi RPG of recent years, there really is no easy way to explain the story without doing it a great injustice...
My favorite series ever, and i have been gaming since 1985, tried so many franchises, and Mass effect sticks out for me.
With the Suikoden franchise as my second favorite.