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Modern shoot 'em up games have come a long way from Galaga and Space Invaders, but at the same time their popularity has dwindled outside of Japan. It's not surprising then that most of the best free shoot 'em ups that are still bringing fun new gameplay to the genre are Japanese-made.

This can make them pretty hard to come by, which is why I've listed some of the best ones here for you. A testament to their quality is that some have actually been commercially released.

The shoot 'em ups listed below are compatible with most PCs. The default controls usually require the arrow keys to move, the Z key to shoot, and the X and C keys for other abilities if applicable.

Warning Forever

Your enemy in Warning Forever (download here) is a single boss that keeps transforming to become more powerful. How it builds up its attacks and defenses in its next transformation depends on how you fought its previous transformation. The boss intelligently adjusts to include more armor and weapons where you focused your attacks before.

It's easy to play Warning Forever over and over as you try to figure out the best way to attack the boss without allowing it to develop protections against its weaknesses. And you can challenge yourself to find as many of the different transformations as possible!

Tumiki Fighters

Tumiki Fighters (download here) is a unique shooter because, once you defeat an enemy, you can fly into its broken pieces to make them stick to your own ship. Your ship will grow, and the individual pieces will shoot extra bullets and add to your firepower. You can get pretty powerful this way, but you'll also become a larger target and it will be more difficult to keep from getting hit by a bullet and losing pieces.

The game was good enough that it provided the basis for Blast Works, a Nintendo Wii game. Blast Works includes Tumiki Fighters and several other free shoot'em ups made by the same developer, as well as a level editor.

Every Extend

You don't actually do any shooting in Every Extend (download here). Instead, you have to blow yourself up to destroy enemies. The idea is to blow yourself up at the right time, when the enemies are close enough to each other that their explosions will link together and score you a chain bonus. It's an unusual gameplay premise, but it's surprisingly fun and addictive to try to make your chains of explosions longer and longer.

Like Tumiki Fighters, Every Extend inspired a full commercial release. Every Extend Extra is an enhanced version of the game released for the Sony PSP.

Cave Shooters

Alright, I'm cheating a little bit with this one. Instead of recommending just one game to you, I'm recommending all of the shoot 'em ups made by the Japanese arcade game company Cave. Cave makes manic shooters, also known as "bullet hell" shooters, and you'll see why that's a fitting title.

In Cave's shooters, the screen is often filled with colorful bullets, sometimes to the point of causing slowdown (but, trust me, slowdown can only help you). Getting through all of those bullets requires precise movement, a little bit of memorization, and a little bit of luck.

These games are mindbogglingly difficult, but it's easy to get addicted trying to improve your skill at them. Because they're arcade games, you can insert as many credits as you like to get through them. But to be among the best players, you'll have to do a one-credit completion: no extra quarters.

Some of the best Cave shooters available as ROMs are DoDonPachi (first image above), ESP Ra.De (second image above), Progear, Guwange, and Dangun Feveron. You can find them for download at a ROM site such as ROM World. To play them, you'll need to use MAME, an arcade game emulator that you can download here. You can read more about how to use MAME here.

BulletGBA

If the Cave shooters are giving you trouble, you might want to turn to BulletGBA for help. BulletGBA includes over 300 patterns of bullets, many taken from Cave shooters. You can select from several different modes to play and challenge yourself to stay alive as long as possible.

BulletGBA (download here) is a ROM for the Game Boy Advance portable gaming system. The easiest way to play it on your computer is to download Visual Boy Advance, a Game Boy Advance emulator. After downloading and opening the emulator, select File and then Open...

Then select bulletgba-5.0.rom.gba.zip from the directory you downloaded it to, and you should be all set to play BulletGBA. You can read more about playing ROMs on your computer here.

These are just some of the best free shoot'em up games. There are a lot of other fantastic games out there. What are your favorites?