A key aspect of Death Angel's gameplay are action cards. Each squad of two has its own set of three action cards. In addition to describing the special abilities of each squad, these cards are used to indicate which of the three basic actions the squad is using: support, attack, or move/activate. Support lets you place a token on any Space Marine that allows him to reroll any die. Attack actions are resolved by rolling a special die; if a skull turns up, one Genestealer is reduced to a pile of goo. The move/activate card allows a Space Marine to switch to an adjacent position, change his facing, and activate a terrain feature (like opening a door).
Players have to be very careful about which action cards to use, as the squad cannot repeat the same action from one round to the next. Since Genestealers spawn like mad, and each squad can only attack every other turn at best, you can imagine that there are some significant choices to be made each turn. It is here that the cooperative elements are perhaps the strongest. In order to succeed, players must use their team's special abilities to the greatest effect, and plan with one another to maximize efficiency. You might decide to swap positions with a Space Marine in mortal danger, and die to a flurry of claws and fangs, just so the other guy can use his special ability to take down a whole column of Genestealers, for instance. The feeling of teamwork, fighting together against overwhelming odds, is quite strong and extremely enjoyable.
If you are a rabid fan of the Warhammer 40,000 setting, a lover of tactical decision making, or you just like co-op games in general, Space Hulk Death Angel The Card Game is absolutely worth a purchase. The cooperative elements are very solid, the art and flavor of the cards is suitably epic, it plays in a very reasonable time frame, and it costs less than $20. I highly suggest you grab a copy and send a whole horde of vile Genestealers to an early grave, or at the very least obtain a glorious and honorable death while trying.