PC Gaming

Hmm, not sure... possibly something from my childhood. Star Control II (now available free/open source as The Ur-Quan Masters is one of my absolute favorites, but I first played it at 6-7 years old -- and English is not my native language, so I can't imagine I understood anything at all about the story at the time.

That or Half-Life is what I usually point to as my all-time favorite games. Half-Life was pretty mindblowing; me and my friends spent a ton with it, so I think it's the best answer for this thread.
Not to mention that we played Counter-Strike so much that even 23 years later, it's likely to be the game I've played the most, despite barely playing at all after my teens.