Magicka

In the category of "fun casual games I've found recently" is a gem called Magicka. It's an isometric beatem-up game that has you slaying legions of goblins, orcs, beasts, and daemons to save the world of Midgård. The difference is that instead of using weapons, you mostly use magic. Lots and lots of magic.

Magicka's magic system is the centerpiece of the game, and it is endless barrels of fun. You have eight basic elements--water, life, shield, cold, lighting, arcane, earth, and fire--and you can combine them in nearly endless ways. There are plenty of rules to this--certain elements can't be used in conjunction with each other, and some of them can combine to produce new ones. You can also cast spells in one of four ways--in front of you, around you, on yourself, or enchanting your weapon. (You do get regular weapons, but they are much less useful than your magic...unless you get the light saber or machine gun)

The basic elements are predictable enough, but combining them is the fun of the game. Combining arcane with shield gives you mines that tick and explode, sending enemies who walk over them flying. Fire is normally a spraying attack, but combining it with arcane gives you a searing beam. Combining fire and earth gives you fireballs; combining earth and cold gives you hailstones that slow enemies. Combining water and fire gives you steam; combining this with lightning and arcane gives you a beam that soaks enemies as it electrocutes them. Ouch. And multiplying elements increases their power, making zapping enemies with deadly lightning a viable strategy. (Especially when they're wet)

Magicka lets you satisfy your deep-seated desire to zap stuff like the Emperor.

Adding to the ridiculousness is the game's simplicity; there is no mana system, so literally the only limit to your magical exploits is how quickly you can cast spells. It makes you feel almost godly, but the game has plenty of challenges to your magical prowess, not the least of which are other spellcasters. These battles are some of the toughest in the game; predicting their spells is essential as one false move can blow you up or send you flying off a cliff. The potential of magic battles to blow up in your face (literally) gets a bit ugly in one particularly frustrating series of battle, but usually it feels surprisingly balanced.

IMMA FIRIN' MAH LAZOR

Besides the basic elemental spells, there are special spells ("magicks") that can be cast by queuing up elements in a certain order. These let you do special actions like making it rain, calling down lightning, (best if enemies are wet from said rain) messing with time, and teleporting. The element system is compelling and practically begs you to experiment with it to see what fun combinations you can come up with. The possibilities let you try many different fighting styles, like running away from enemies and luring them onto mines, gathering them around you and casting area-of-effect spells, or just lasering everything.

Spell-slinging galore!

Besides its fantastic magic system, Magicka also benefits from some truly fantastic writing. If you enjoy less-than-serious medieval adventure games like Kingdom of Loathing or Munchkin, or if you enjoy the humor of games like Banjo-Kazooie, Magicka is worth checking out for its humor alone. The characters constantly spew cultural references, break the fourth wall, and in general constantly find new ways of making you laugh. So far the best I've seen is a boss fight that has James Bond, Star Wars, and Lord of the Rings references, all within a few minutes.

One example of the game's countless references.

Your narrator and giver of advice is a fellow named Vlad who is most definitely not a vampire. You also get a fairy companion who is an obvious parody of Navi from The Legend of Zelda: Ocarina of Time and frequently gives you gems like "Maybe you can cast spells on enemies?" and "If you die, I will hate you!". Even the game mechanics have references; when casting beam spells, don't cross the streams! My only complaint of the humor is that it seems a little too reliant on pop-culture references, as opposed to original silliness. But it's great fun all the same.

Your fairy companion is an endless source of obvious advice. And yes, you are carrying a Master Sword.

If you got Magicka during the 75% off sale like I did, congratulations. Otherwise, it's certainly still worth the $10 purchase. The adventure is 10-15 hours long, but the fun combat, humor, and endlessly deep magic system encourage heavy replaying, and there is are many DLC expansions to be had. If you can convince your friends to buy it as well, it also has online co-op and PvP!