Flashback was introduced to me by my friend Ben. I think we both downloaded it off of the old school "smuggler" bbs (original pirates). This game was epically difficult for me at the age that I was playing it (probably 11 or 12).
I'm not sure I ever finished it but my brother said he recently replayed it and got to the ending. It was the kind of game where one shot killed you, so in the difficult parts it became more strategy than action.
Most distinct about Flashback was the graphics and art design. The fluidity of the character movements was unheard of for its time, and the unique moves like crouching, rolling and firing your weapon still look good.
The art design was great too, the levels varied from cyberpunk cities to alien jungles to goopy caves, and the cut scenes had a cool 70's sci-fi style. Here's the intro to the game:
This was a very influential game for me and that first level video brings back great memories.
Delphine Games, which was a French company, released a sequel to Flashback which I never played, though apparently it wasn't particularly popular. Delphine planned to release a third sequel but the company went bankrupt.