Cosmic Encounter is the game that is supposed to have inspired Magic the Gathering. Simply Cosmic doubles as the simpler starter version and as an upgrade for the original game. Cosmic Encounter is a game where you have to colonise the other players planets. You fight by playing cards, there are also a number special cards that you can use to change or break the rules. Every player also has one special power: a special rule that only she can use. The game really resolves around getting right combos of cards, tactics and special powers. It is very much a 'gamers game', a game where you need a good understanding of the rules and an eye for their interaction. It may take a while to get the hang of it, but when you do it is tons of fun.
When looking for this game be careful, though. Hasbro has put out a new version also called Cosmic Encounters, this version pales in comparison with the original one. For some reason they have left out a number of game concepts, which drastically reduces the number of options and combinations – and thus has rather poor gameplay. And I happen to like the simple and abstract design of the original. So if anyone is willing to sell me the classic Mayfair edition let me know!