The premise should be familiar to anyone that's played a fantasy adventure game before. An evil old wizard is trying to destroy the world and only you (and three other players) can stop him. The tired setting isn't a handicap for Magicka, though, as it allows Arrowhead to satire some of the genre's conventions and most iconic moments. (For example, a hidden area will have you grabbing a "Master Sword" from a stone pedestal, with Zelda-esque music playing in the background.)
What is unique is its gameplay, which focuses on casting element-based magic using the right analog stick. Various elements are assigned to eight directions on the stick, and hitting the analog in a certain direction queues up a spell. The placement of the various elements (and the iconography used to represent them) isn't particularly clear, making Magicka not the most intuitive game to play. However, these elements can be combined and stacked to create interesting spells -- and the addition of co-op multiplayer makes casting magic even more dynamic.
For example, a single player can select both fire and water to create a steam attack. You can add earth to that same spell, and you'll be able to cast a bomb that explodes in steam. You can also stack the same element to create a more powerful version of a spell. For example, fire combined with fire combined with fire makes for (get ready for it) really big fire. The downside of using heavier spells is your character will move much slower. During battles, you'll not only have to think about what elements to use, but how to use them. During boss battles, for example, being slowed down may leave you incredibly vulnerable.
Magicka is at its best with friends. Each player has access to the same spell wheel, and friends and enemies are affected by spells equally. It's a lot of fun to (accidentally) set a co-op buddy on fire as you try to take down a swarm of encroaching enemies. With up to four players playing simultaneously, it's possible to create some diverse strategies. For example, every player can use a different ability in tandem: one player can set up a barrier, while another casts an offensive spell, while another focuses on healing the party, while the final player uses melee attacks. Other times, it may be smarter for everyone to simply cast the same spell on the same target simultaneously.
The small snipped of Magicka I played showed a lot of promise, thanks to its simple and fun-to-use magic system. It's a simple title, perfect for a co-op romp on Live. We're hoping the final game demands using the various elements in more original ways. We already saw a hint: a hidden path that can only be accessed by freezing a river with ice, for example. Paradox Interactive is aiming for a Q3 release on PC, with an Xbox version planned (but not necessarily confirmed).