It's sort of a misnomer to call Cosmic Encounter a board game. In a real way, it's a dozen or more related games in one box. The hundreds of setups that can emerge from playing despite simple rules is impressive.
In the game you play an alien form that wants to rule the universe, and so must spread across the stars to many different worlds. Each player owns a few planets, and each planet has a few ships on it. You want to get your ships to five different planets controlled by other players.
Every turn, you draw a card to determine what player's star system you can try to invade. Players choose a number of ships available. Each player also has a hand of cards; these usually have a number on them, and you add them to the number of ships you're risking in the fight. Loser loses ships, and winner gets to place them on a planet.
In addition, there's also the deceptively tricky "Negotiate" card that can be used to broker deals instead of fighting. But you can also lie about what you're going to play and get a quick hit in, albeit while conceding a few things to your enemy.
That's the core of what you're doing in the game normally. There are some additional cards that affect things you can play, various special abilities and whatnot.
But there's a catch, a big catch.
Every player is an alien species, each with its own special ability that affects the game. And by affects the game, I mean utterly changes how that alien species plays.
Take for instance, the "Losers." Any time they would normally lose a fight, they win that fight instead. They lose if they would have won.
Or the "Zombies." They can bring dead ships of theirs back to life, and as part of negotiation, can bring back other players' ships from the dead.
And keep in mind, every single player can do something like that.
I've played games where two players have won simultaneously. I've played games where everyone was a different species at the end. Sometimes a whole new planet will form in your star system due to lost alien technology.
There's really no telling what'll happen, and that makes Cosmic Encounter one of the most compelling games you'll ever play.