Captain Blood draws you in with its plain weirdness and keeps you hooked by being a surprisingly deep and compelling adventure (and it's ultimately not as weird as you first think - it just has a very unique presentation).
The basic(!) premise of the game is that Captain Blood - a game designer working under a pseudonym - has been sucked into his own creation and split into 30 clones. He has to travel the galaxy searching for them before he deteriorates out of existence (he needs to reabsorb the clones to make himself complete again). Over the past 800 years he's managed to track down 25 of the clones and it's now up to the player to help him locate the last 5. To do this he has to make friendly contact with a number of alien individuals and learn the co-ordinates of the planets where he'll find them.
The most memorable and striking part of the game is the contact with the alien races. Communications are carried out through a series of icons which represent emotions, ideas, threats, requests, etc. and can be strung together to form basic sentences. In this way Blood can coerce the contacts into aiding him in his quest. As he deteriorates over time, Blood's onscreen hand (the player cursor) becomes more and more unstable.
I don't think I really appreciated it fully back when I first owned it for the ST - I just tended to enjoy the planetfall sequences and blow planets up, but over the years its appeal to me has grown enormously. There are some rather lavish hyperspace and planet-destruction effects, and my favourite part of all - piloting a probe down to the surface of a planet - is done in a fast wireframe fractal style.
Captain Blood is one of those games that just oozes atmosphere and completely pulls you in, but there's also plenty of game in there to get your teeth stuck into. Truly unique stuff.