At it's core, Elder Sign is a dice rolling game, and the random element of the dice adds much to the tension. Six different adventure cards are available to explore each turn, each requiring certain combinations of dice. You'll usually be rolling six green dice, marked with faces with providing varying amounts of clues, and also a skull, a scroll, and a horrific tentacle. Using the adventure card above as an example, you would have to roll three clues first, then two skulls, and finally two scrolls. It can be very hard to do this, especially since each time you fail, you have to set one die aside.
Thankfully, special cards can be turned in to roll the yellow and red dice, too. These dice have better faces than the green ones, providing many more clues when rolled, and also a wild symbol face that counts for anything. Rolling these special dice makes completing the tasks much easier, so managing them well is key. If you successfully meet the requirements of an adventure, you earn a reward, which might be drawing a special card, or earning a precious elder sign. Failure has various effects, including losing sanity, stamina, or putting a monster on the board.
The cooperative elements in Elder Sign are not particularly strong from a mechanical perspective. Players can assist a player who has failed a mission, which allows them to set dice aside in order to make the dice rolls for later tasks easier. Apart from this system, and the healing mechanics discussed earlier, teamwork seems sparse. However, the real cooperation comes in making decisions as a group. Deciding which adventures to go on, playing to individual strengths, and working together to plan the best defense are keys to success. In this sense, then, Elder Sign has strong co-op themes.
Though it lacks the depth and overall meatiness of Arkham Horror, Elder Sign is still a very good game. It is particularly well suited to playing with more casual gamers, due to the appeal of the dice and hour-long game length. The theme is really where Elder Sign shines; you'll have a superb sense of adventure and excitement as the unspeakable horror of a Great Old One draws ever closer.