I played it.
Sadly my books did not survive multiple moves. All my GB, Paranoia, James Bond 007, Top Secret, TimeMaster, and a few other RPGs got wet and insect infested in storage. Sad drow.
I had the box set and a few expansion books and modules. Its been so long I cannot recall the mechanics of the game, but I do recall several funny game instances.
One memory is of an adventure where garbage cans become animated. One of the garboids swallowed the McGuffin and a 'buster reached in its mouth to retrieve it. I told him he grasped something soft, wet, and wriggling. He trid to pull it out. It wouldn't budge. He kept trying and the garboid kept mumbling, louder and louder, "Nwet gho'un maton." After a few minutes of this, the GB let go and asked the garboid what it was saying, "I said, Let go of my tongue!" Hilarity ensued. This is what passed for high brow humor to 13-year-olds.
The garboid became that GB franchise's Slimer. They named him Rusty.
Before West End came out with the GB RPG, a friend and I were working on one based on a heavily modified version of the Top Secret rules. This was before home computer were common,. so we had reams of legal pads and notebook paper filled with ideas, rules, ghosts, etc. No idea what happened to those papers. Drow sigh