A great example of the blend of theme and mechanics is the face hugger. When this Hive card is revealed, whether by scanning or simply escaping into the combat zone, the current player puts the card on the table in front of them. Any player can attack it, and it is usually very easy to defeat, but there is a time limit. By the end of the next player's turn, if the face hugger is not defeated, it is discarded, and the unfortunate owner adds a chest burster card to their deck. At some point, inevitably, deck is reshuffled and every draw becomes a potential "Game over, man!" scenario, as the chest burster card immediately kills the player when drawn. I was on the receiving end of a chest burster, and trust me, it's a delightful tension, a wonderful mechanical element mirroring the famous situation from the movies.
Another addition to Encounters that was missing in the original Legendary is Player Roles. These are special cards selected as the game begins that give each player a different power, like the scanning ability of a Scout or the healing of the Medic. Roles serve to differentiate the players from one another, increasing the feeling of camaraderie and teamwork. Healing is a new mechanic, too; each role can take a different number of wounds from the Strike deck before the player dies. Aliens, unlike Super Villains and their minions, actually fight back instead of patiently waiting to be defeated before escaping the board. It's far more confrontational, and again, adds to the tension considerably.
A wide variety of scenarios and play variants are included, which should extend the lifespan of Legendary Encounters over its predecessor considerably. The masterminds and schemes of Legendary were always a bit disjointed, and felt largely the same. (Exactly why would Loki and Spider-Man's foes team up to rob a bank?) In Encounters, the feel is much more thematic, with the characters and situations from each movie as well as others available. You can reenact the original encounter on the Nostromo, or the faceoff with the queen, without fear of being taken out of the theme when something that doesn't fit pops up. Variants for traitors and player-controlled aliens only add to the replayability of the game.
The cooperative aspects of Legendary Encounters are far stronger than the earlier entries in the series. The healing mechanic mentioned earlier is one good example. Killing face huggers before they attack your neighbor and spawn a chest burster is another. Perhaps my favorite is the ability of some cards to be spent to help other players. Often, a player comes up one or two wounds short of killing the target, but if any other player has one of these shared cards, they can use it to get the job done together. There's no penalty for doing so, either, since these shared cards replace themselves by allowing another card draw when played. These little touches add considerably to the feel of co-op in a genre often criticized as being "multiplayer solitaire".
I found Legendary Encounters to be a fantastic improvement over the original, and a very strong game in its own right. Such a tight blend of mechanics and theme is almost unheard of for a deckbuilding game. You really dread seeing what turns up next, and working together is the only way to win. I highly recommend Legendary Encounters to any fan of co-op, but especially those who enjoy the Aliens movies. I can't wait to see what they have in store for the Predator...