It's hard to deny the success of the cooperative shooter in a post-Left 4 Dead gaming world. Getting to shoot stuff alongside your friends? It's a formula that, quite frankly, is immensely satisfying. The PlayStation Vita, with its twin-stick layout, is finally the device that can deliver this experience to the palm of your hand. But don't take my word for it; the Vita attempts to prove this with Unit 13, a co-op cover-based shooter developed by Zipper Interactive.

The premise is that you'll control a squad of six mercenaries, embarking on an assortment of missions. (Yeah, there's no real story arc to speak of here.) Each of the game's 45 missions allows you to choose one of the six available operatives, though there will be a suggestion at the mission select screen to let you know which operative is preferable for that particular mission type. You see, each has a slightly different loadout and stat balance, so, for example, one operative might be better at stealth, while another might be better at run-and-gun tactics.

At the end of each mission, you'll be given a score and a star rating. If you're connected to PSN, you'll also get to see where you rank on the online leaderboards. This provides a little incentive to go back through each mission and try new strategies in an attempt to maximize your score and climb through the rankings.

The fact that the game is broken up into these bite-sized missions makes it incredibly easy to pick up and play in fifteen-to-thirty-minute stretches, which is incredibly well-suited to the Vita's portable nature. On the other hand, if you have the time, this also keeps you itching to play "just one more mission." It's a formula that just plain works for the Vita.

Unit 13 is surprisingly competent for a handheld shooter. The controls don't merely work here; they feel surprisingly great. The control setup is remarkably similar to Uncharted—with the exception of not having a dedicated jump button—which isn't at all a bad thing. The face buttons are incredibly responsive as well, and I found myself impressed at just how quick and satisfying the melee attacks feel. In fact, even the touch-based commands feel incredible due to their location on the screen. For instance, as you approach a bomb, the touch command for disarming it shows up on your screen right next to the left analog stick. Also, when you approach a waist-high piece of cover, you can leap over it with a quick tap. This means that even face-button junkies like myself will have no problem bumping the touch commands with a thumb without having to awkwardly reposition their hands. It's the smoothest and most intuitive use of touchscreen integration I've seen on the Vita so far.

However, I do have some complaints about the controls. The most important is that firing from cover isn't as slick as you're probably used to if you've been playing a lot of Uncharted or Gears of War. Taking cover around a corner keeps your character positioned further back along the wall than you'd expect, and you can only fire from cover when your character is aligned just right. This will undoubtedly lead to frustrating encounters where you feel like you should be able to fire your weapon yet you simply can't. In fact, in the later missions where the difficulty level gets pretty high, expect to die quite a few times due to the awkward cover mechanics.

My other complaint—and this is more of a personal nitpick rather than a true complaint—is that I would have liked to see a face button assigned to hopping over cover. As I mentioned earlier, the touchscreen commands are surprisingly well-implemented, but still, not being able to leap over cover with a face button feels weird to me. Nonetheless, it's not something that ruins the game by any means, and it's not difficult to get used to.

Aside from some strange little quirks, the enemy A.I. is halfway decent. It's not just the dialed-up aim accuracy that makes the game challenging—though, these guys definitely know how to shoot—but the fact that your enemies will implement a bit of strategy, like not popping up from cover in a predictable manner. Also, even though the game features a lot of stealth missions, don't expect the narrow cones of vision or totally clueless guards you would expect from a Metal Gear Solid title. No, these guys don't mess around. For example, planting a bullet in a wall, even with a silenced weapon, will draw suspicion from your enemies. And don't expect to pop a silenced headshot into a guard without other enemies in the area taking notice. As a result, many of these missions require careful planning and honed skill.

However, there are some notable flaws in the A.I. For example, some enemies will stand completely still for a couple seconds after the guard standing next to them gets a silenced bullet in the brain. This gives you an unrealistic advantage, as you can quickly pop off a headshot before this enemy goes into alert status.

The graphics are decent for a handheld title, though with nowhere near the level of detail that, say, Uncharted: Golden Abyss displays. The environments look good enough, though some of the character animations are pretty clumsy. (The death animations in particular are just plain creepy, as your character maintains a stiff and completely unconcerned facial expression throughout.)