Star Realms is a deck building card game in which two or more players battle it out, attempting to destroy the other's fleet.
Each player has a fleet of ships and space stations which they build to maximize defense, attack, and profit. A turn consists of drawing a hand of five cards and playing them to your best advantage; many cards have synergy effects that only appear when played on the same turn as another ship of the same faction; others have a choice of two possible actions; some can be destroyed for a special actions.
The game follows the standard deck-builder format, and will be easy to pick up if you have played Ascension or Dominion (and, indeed, even if you have not), but makes a significant change in that it does not use victory points to keep score. Instead of having to count up your cards and counters at the end, you know who has won because they are the only ones left alive.
There are no monsters in Star Realms; all attack points are spent directly on your enemies. This is complicated by the addition of defense cards that act as shields and cards that gain players extra health. Once your opponents have zero health they are dead, and you win.
Star Realms is one of the easier and more straight-forward deck builders, but doesn't lose anything because of this. It is small, easy to set up and easy to teach, but remains enjoyable even after your 10th or 30th game. I personally also like the spaceship theme more than the usual deckbuilder fantasy/superhero themes, and the art on the cards is pretty decent (standard SF high representational art).
There are five small expansion sets of additional cards for Star Realms, and a larger expansion that can work as a stand-alone game, Star Realms: Colony Wars. There is also a related game by the same company and author that shares the same basic mechanic called Cthulhu Realms.