Shmups, especially vertically scrolling ones, tend to be extremely difficult, peppering the screen with elaborate waves of bullets, and asking the player to weave between them like a robber entering a laser-strewn bank vault. Guardian Sphere (opens in new tab) is a little easier, a little less bullet hell, and a perfect way to become acquainted with a slightly daunting genre.
Playable by one or two players (offline), it's a thoroughly traditional shoot-'em-up except in two ways. The first is that there are no high scores, which is admittedly a little odd, and the second is that you can trade in your health to buy upgrades.
The game was made for a recent Ludum Dare (theme: your life is currency), and developers Pixel-Boy and AAA chose to take that theme literally. Your health consists of a number of colourful spheres, dropped by enemies, that deplete Sonic-style, every time you take a hit. But you can also use them to buy a frankly enormous range of upgrades at each of the shops in each scrolling stage, including extra bullets, bigger bullets, homing bullets, and other stuff just as good, but not to do with bullets.
It feels like a roguelike, but without the extreme difficulty, and with less replay value. However, I thoroughly enjoyed blasting my way through the slick, and fully featured Guardian Sphere (opens in new tab).
For more great free experiences, check out our roundup of the best free PC games.