BTSX is an abbreviation of "Back To Saturn X", which a series of map pack (or WADs) for the video game Doom 2, it's often praised for it's beautiful architecture and visual for a map pack build in a 1994 game engine, but it's also sometimes criticised that the maps are so consistently well done that it felt repetitive.
the phrase can be used to describe a game level or a series of things that's so consistently perfect, it's repetitive and unintuitive.
This game's level had gotten BTSX Syndrome, it's good but ultimately boring.
Nickname given to bales of marijuana thrown overboard or out of airplanes. Origin is reportedly from members of the US Coast Guard in the area of Southern Florida.