First non-D&D RPG you played.
I never played a non-D&D RPG until I got involved with the 2E group. In fact, 2E wasn't the first game I played with them. It was a homemade d6-based game of paranormal investigation that they called Nightwatch. Character templates (they didn't use the term "class") ranged from mundane sorts like law enforcement officers, scientists, and journalists, to werewolf and vampire hunters, mystics, and witches. My character was an FBI agent named Jack McMillan, who was a little out of his element around supernatural weirdness.
The character templates had some balance issues, but overall it was a pretty fun game. At one point they were planning to publish it, and had a website and everything, but now that's gone, and I've never heard anything about it since. Kind of a shame, really.