GURPS was designed for modularity - the "G"enteric in the name. There was a basic ruleset, and then you bought the adaptation rules for whatever setting you wanted to take the ruleset into/toward. Like GURPS-Cyberpunk (that got poor Steve Jackson in trouble with the Feds; they called a game about hacking a "manual for computer crime")... there were GURPS addenda for all the typical RPG settings, like high-tech/sci-fi, fantasy, superhero, modern/espionage, and supernatural/horror.
Shadowrun's fun, but if you want to play a cyberpunk game without the neo-fantasy elements melded in, GURPS Cyberpunk is one of the best.
Of course, I also like their Illuminati card game - always tell tinfoil-hatters to go play
- and the Munchkin series, which pretty much mocks the "munchkin" play style of many modern RPGers, where uber gear and loot rules uber all.