Flyboys in the Age of Robots.
Conceptually, Dark Void Zero is a pretty unique concept; taking the concept of the game Dark Void and fitting in onto the DSi with a fake-retro sprite art style is interesting even on a superficial level. The joke is that Zero is supposed to be the "original" game that the Xbox 360/PlayStation game was based on, when it's actually the other way around. Gags aside, Dark Void's gameplay transfers remarkably well to a simpler layout. In true retro fashion, you only use the D-pad and the A (jump) and B (shoot) buttons to play the game. When you think about it, the third-person shooters of today are really the modern incarnation of the NES-era side-scroller, so it's not surprising that the controls work as well as they do.
Think of it as cross between Mega Man and Contra, except that the gameplay revolves around using a jet pack. Most of the areas in the game are inaccessible until you find a jet pack, most of combat will have you flying around to avoid bullets rather than jump over them, and the boss battles are completely devoid of terra firma. You can fly around as much as you like without worrying about fuel, but certain areas will make your jet pack unusable. The game changes up the pace of combat quite often, which is impressive, given the technical limitations of the game.
The shooting and flying work very well together. There's an appropriate lag when you turn directions while flying, and most of the enemies know how to avoid your attacks. The standard alien robot enemies might not be too difficult, but some of the flying enemies and later humanoids will test your dexterity and reflexes without turning the game into bullet hell. There's something very nostalgic about this sort of rewarding twitch gameplay. The structure of Zero also abides by retro standards, complete with limited lives, health, and oppressive save systems. You have a limited number of lives and, and if you lose all of them you must restart the entire level, though there are checkpoints should you lose a life near them. You can find extra lives as well as different power-ups, though you can only hold one gun at a time. The game is nothing if not dedicated to reminding us of how games used to be.
But perhaps the most memorable thing about Dark Void Zero is its chiptune music. There are all of three songs in the game (one per level), and with as much as they're repeated, you'll be lucky to not find yourself humming them even after you beat the game. They do a good job of invoking both the 8-bit days and the Rocketeer vibe at the same time. Dark Void Zero's biggest flaw is that it's very short game --on easy difficulty, I beat it just over 3 hours --, but for 5 dollars, it's not a bad value, especially . If you happen to have some DSi points lying around, this is a game you should consider using them on. Or hell, it just might be worth it to go through the process of buying more points.