In Cannon Brawl there are two castles, one positioned on each side of a peaceful valley. This circumstance is, of course, intolerable. There really ought to be just one building, and your job as the player is to bring about such a future, even as your opponent--whether controlled by a second player or just the devious computer--tries to turn your base into a pile of rubble.

You may recall other games that employ a similar setup. CastleStorm comes to mind, for instance, with its pleasing blend of crazy action and tower defense mechanics. While past games prevent this new effort from offering much in the way of surprises, though, lingering familiarity ensures that genre devotees will be able to get right down to the business of castle demolition.

When a round begins, you find your castle positioned near the edge of a cramped map. As rousing battle themes pipe from your speakers, you stake your claim to verdant hills and blue skies, to deserts so yellow you might wish you could vacation within one. Floating landforms populate the foreground, which you and your opponent can blast away with shots from cannons, lasers, and other such contraptions, almost like you might in a Worms game. There's no turn-based respite, though, in spite of the cheery vibe; you make your decisions and you execute all plans on the fly, with as little hesitation as possible. Speed is a necessity, or else you might line up a beautiful shot just in time to find out that your laser tower has been blasted to smithereens by a roaming ball of explosives.

In a game of this sort, an intuitive interface is vital. The developers at Turtle Sandbox put the player in charge of a flying airship, and that approach pays dividends. Using your keyboard or a gamepad (the latter works particularly well), you can pilot the ship anywhere you like without having to worry about taking damage. You must make quick trips back to your castle to grab new structures, then plop them down at key points along the map. Your expansion options are limited at first, until you have placed enough surveillance balloons, mining camps, and other such attractions along the way. Then you can dock with a given point of interest--for example, a rocket launcher--and direct its actions. Although there are times when dropping buildings and docking require excess fiddling, particularly when too many structures are in close proximity, the interface works beautifully and allows you to work at the brisk clip gameplay demands.

There's no turn-based respite, though, in spite of the cheery vibe; you make your decisions and you execute all plans on the fly, with as little hesitation as possible.

Naturally, there are complications. Though some buildings regularly perform a specific task without your direction, most of them are useless without orders. They also must go through a cooling period, which means you can't simply rely on a single device to secure victory. Instead, you constantly must move your airship from one spot to another, adjusting for rapidly evolving combat and a changing landscape.

As the game begins, there are only a few offensive measures available. Even once you advance far enough in the campaign that your list of options expands, you can bring along only a handful of tools. You almost always have to survive without something important, and your computer opponents are great at adapting to diffuse any winning tactic you might employ. This means that if you try one technique in a round and it fails for a particular reason, switching to a different one the next time around is no guarantee that you'll find success: the AI could easily adapt and catch you by surprise in some other manner. Such adaptations keep matches interesting, because you always have to stay on your toes and watch for attacks from a few potential directions even as you replay the same map.

You also need to decide which airship captain to bring along for the ride. Each one grants a different sort of boost. One lets you form repairs if you get close to a building that has taken damage. Another one allows you to start with extra gold and also enables you to harvest resources more efficiently. The first captain you meet, however, may be the best one of all. She reduces the cooling period for everything, which becomes so important by the end of the campaign that any other captain feels like a handicap.

One problem with Cannon Brawl is that it gives players access to a bunch of cool toys, but most battles ultimately play out in the same manner. You start by claiming as much territory as possible and building mines. Then you drop a few towers and dart between them, firing shots at your opponent and hopefully taking out his or her resources before the tide of battle can turn against you. Your greatest ally besides speed is momentum, and the combination of the two often wins out against the more creative and interesting approaches that the the game allows you to explore. When there's little reason to rely on more than a few basic turrets that are dependably efficient, unlockable content is nothing more than window dressing. Even in online matches, simple strategies easily overwhelm opponents using more varied forms of weaponry. Over time, you earn experience points that allow you to access additional pilots and structures in the armory, but when simple tactics are so effective, it's difficult to drum up the enthusiasm required to unlock them.

The game's difficulty level already feels punishing enough when you play on the higher settings, because suddenly your opponent moves with a distracting (and distressing) level of precision. Almost before a round even begins, it throws up shields, health-regenerating towers, and upgrade cannons. Meanwhile, you might still be struggling just to get a few balloons in the air so you can start mining. Such battles commence with momentum and resources already working against you; the obstacles are hardly insurmountable, but if you want a fair conflict, you're better off finding human opponents instead.

Cannon Brawl is interesting enough to enjoy in small doses, but it wears out its welcome once you realize its efforts to inject a little variety into the proceedings only go skin deep. If you can find a few friends at a similar skill level to challenge, you'll likely enjoy several hours of strategy mayhem. Otherwise, you're better off in another castle.