Solid Snake has jumped genres for the first time in his illustrious career with Metal Gear Acid, a strategy game that's arriving just in time for the launch of the new PlayStation Portable. Acid supplants the familiar stealth action gameplay of the Metal Gear series with...tactical card-battling? Yes, strange as it may sound, Acid's satisfying turn-based strategy is a great fit for the series' trademark high presentation values and quirky narrative style. It's not an easy game to get into, and if you're just looking for a portable stealth action Metal Gear, you'll need to keep waiting. But once you get a handle on the core mechanics, you'll find in Acid a rewarding game of strategic stealth combat coupled with a quirky, intriguing storyline and some neat points of nostalgia for the longtime Metal Gear fan.

Like chocolate to peanut butter, Konami got card-battling in our Metal Gear--and it's darn tasty.

The game seems to take place outside of the main Metal Gear timeline, since almost all of the characters are new. Poor old Snake is never able to get any rest--he's once again called out of retirement to handle yet another sticky situation, this time by a commander named Roger. Mercenaries have overtaken a corporate-sponsored research facility on the African Lobito Island, demanding that a secret military project called Pythagoras be handed over to them. Their bargaining chip is a hijacked airliner currently circling the skies, which happens to contain a senator who's a front-runner in the upcoming American presidential elections. By the way, this plane has been hijacked by a couple of murderous talking dolls. What the hell is going on here? Snake is sent to infiltrate the Lobito complex to find out. With the help of Roger and a child psychic named Alice, he's tasked with recovering Pythagoras and defeating the mercenary group. In true Metal Gear fashion, this is only the beginning of the tale. The storyline wends its way all over the place throughout the game, pitting multiple factions against each other and introducing new characters at a rapid clip. Some of the players in the story may not be what they seem...even Snake himself. Metal Gear Acid tells its story with still artwork and text, rather than employing the same sort of over-the-top cutscenes and voice that helped make the series famous.

At first glance, Acid looks a lot like your typical Metal Gear. You view the action from the familiar top-down perspective, and the levels are set in dimly lit military camps and greenish industrial complexes similar to those in past games. But you can't spend more than 30 seconds with Acid before you realize this is a radically different game. Missions proceed in turn-based fashion, with each level laid out in an invisible grid that you'll navigate one square at a time, killing or sneaking past the enemies that stand between you and your objective. The focus of every Metal Gear game is stealth, and despite its turn-based structure, that focus remains in Acid. This makes tactical planning highly important, as you'll need to map out your strategy in advance to either take out foes or get around them without being caught. Raising the alert doesn't always spell immediate disaster (though sometimes it does), but it will always make your life more difficult.

The card-combat engine in Metal Gear Acid is thick with depth and complexity, though it will likely take you a while to figure all of it out. The basics are simple enough: You have a store of cards from which you'll build a deck before each mission, and at any given time you'll have a hand of random cards drawn from that deck that represent the actions you can take during the present turn. Some cards are designated solely as move cards, which (obviously) are used to move you a set number of squares around the board. Use cards represent items that you can use immediately during the turn, and these range from offensive weapons to stat buffs and other peripheral effects. Finally, equip cards can be attached to a finite number of equipment slots so you'll have them ready at all times. For instance, you can equip an AK-47 card and then apply any other weapon card with the same ammo type in order to fire it; meanwhile, while the gun card is equipped, you have a chance of counterattacking with it whenever an enemy hits you. Most use and equip cards can also double as move cards, so you'll never be stuck in a stationary position, waiting for another chance to move to come up in your hand.

Snake's latest summons out of retirement sends him to Lobito Island to stop a group of marauding mercenaries.

Beyond the basics of using all these card types, the game gets a lot more complex, and unfortunately it could do a better job of explaining its higher-order mechanics. Each card has a numeric "cost" that essentially describes how long it will take you to recover from using that action, so "time" might have been a better descriptor for this value. The game initially tells you that you fire an equipped weapon by using an ammo card of the same type on that weapon. In reality, there are no ammo cards; what it actually means is that you can apply another weapon card with the same ammo type, which isn't made very clear. The game's manual does a passable job of explaining these mechanics, but the sparse in-game tutorials could have used clearer language to make things more obvious. The saving grace of this lack of explanation is that eventually you'll get the hang of all the systems at work just by beating your head against them, if nothing else. The game is certainly unforgiving, so you'll pass through a trial by fire of sorts as you retry tough missions time and again and get a feel for the mechanics. When everything clicks, finally, you'll be pleased to find out exactly how many different options you have for surpassing obstacles and completing missions.

In fact, Acid's dynamic combat model allows for a wealth of strategic possibilities. The further you progress through the game, the more techniques and abilities you'll be familiar with, and the more you'll be up against seemingly insurmountable odds.