Fail-Safe is my absolute favorite Jon Ingold game. The game has an unusual plot device which you discover quickly. I won't talk about it in this review, because the game is strong enough without it.
The game is set in a damaged spacecraft that must be explored. The difficulty and fun lies in trying to figure out how the spacecraft actually worked.
The game has some timed events (which are fun but hard) and some hard-to-find exits (which is annoying but fun if you can find them).
This game can be played enjoyably multiple times and has a several, interesting endings.