Vikings. If my understanding of this period of history is correct, and I have no reason to believe that the 1973 cartoon series Vicky The Viking was lying to me, they're like amphibious pirates on Spring Break. If any race prepared the world for the invention of the internet meme by inventing bacon, it was probably the Vikings, roaring enthusiastically into a horn as they sliced it off the pig.
During the single player campaign of CastleStorm, it looks like Vikings are the 24-hour party people at the gate - the marauding aggressors. It's your inexplicable job to stop them. As the moustachioed King of the Castle, you've got three ways to fend off the horde of awesome, and each of the gamepad's face buttons offers its own contribution to your overall strategy.
On the Green A is your ballista. Aimed with the left thumbstick, it can loaded with anything from arrows, rocks, grenades and flatus-bloated ovines. The sheep is a cheeky reference to the classic whimsical Worms weapon, and the CastleStorm story is full of these cultural winks. Game of Thrones, Angry Birds, Skyrim - it's nothing if not aware of the world around it.
Each weapon has a different cooldown, giving you a constant stream of basic javelins, and a more occasional use of the more explosive or exotic stuff. You can aim the ballista at enemy troops or the enemy castle, and the single-player campaign brilliantly finds endearingly plot-driven ways to encourage you to test out every tactic, ammo type, and troop unit.
Speaking of which, you don't want to spend all your time firing those arrows. On the Blue X, you've got your troops. The ultimate goal of the troops is to capture your opponent's flag, which along with levelling the enemy castle is the way of winning a match. They're also a good distraction: your enemy can't pelt your castle with grenades if his ballista is busy dealing with a castle that's up to the bloody crenelations in Donkey Riders. Bought with a simple resource system of constantly accruing food, your castle can spit out a constant and varied array of AI-controlled units.
Archers stay at the back. Knights stride forwards, supported by Priests. Griffins hover above, delivering powerful strikes, but prone to ballista fire and unable to nab the flag. Golems are slow, expensive, but absolute sods to kill off. The range of units open to you is defined by the rooms in your castle, and becomes more limited as your rooms get destroyed - but more on that later.
Finally, on the Yellow Y, we've got magic. The first and most notable magic trick is the Hero Summoning spell, which lets you conjure and control a strong unit on the line between to the two castles. Magic is the most varied group, letting you can summon spectral swords, shields for your castle and unites, and healing spells.
That just leaves humble Red B, which hasn't been wasted: you can tap it to order everyone to adopt a defensive position. Useful if you notice the enemy ballista has just aimed a cluster of javelins at your Priests.
CastleStorm is so simple, yet so beautifully designed and craftily nuanced, it's an absolute pleasure to play. It hits the same compulsive nerve as a mobile game, with a star-ranking that rewards accuracy, difficulty level, and a varied range of side-missions. This also gives you a good reason to go back and start again on Hard. In the longer-term game, you're constantly accruing gold that you can spend on upgrades to your missiles, troops, castle rooms and magic spells. The upgrades are pretty shallow - mainly damage boosts and cooldown reductions - but it does let you build your own play style.