Magicka: Vietnam
It's more Magicka, with more guns! And I would say that this is the end of the story, but to be truthful I'm actually overselling it. The Vietnam "expansion" adds a total of two Challenges to the game, one of which is just another wave-based survival arena. The other is the Vietnam mission, where your goal is to shoot some goblin-cong, destroy ammo caches, rescue POWs, and ultimately defend an extraction point until a rescue chopper rolls in. It isn't integrated into the game's campaign mode, and other than a paragraph-long introduction from Vlad, isn't narrated or at all embellished with Magicka's game-industry satire. I mean, not counting the fact that this is a Vietnam expansion.
There's a new magick in the form of an aerial napalm strike, which is awesome, but since the Vietnam mission is a challenge instead of a story mission, your other magicks (meteor storm, lightning, et al) are all unavailable. Magic in general is harder to use, since all the enemies have guns, and, like the annoying bow-and-arrow assholes in the main campaign, keep interrupting your shit all the time. That said, the gun selection that you can use - from the main game's M60 and other automatics, to bolt-action and burst rifles, and an RPG launcher - does put an interesting twist on the core gameplay.
It is more Magicka, but not very much more. It's easy to say that $5 is a rip-off for what amounts to a single mission. On the other hand, and this is a two-fingered hand, 1) the main game was already really cheap and 2) it's still only five bucks.
Progress: Died at the end (too many mortars!)