INTER-GALACTIC JEWEL THIEVES

This is a shoot 'em up where the ship is controlled with the keyboard and shooting is controlled with the mouse. 
You can play it by yourself, or get a friend and have one player control the ship and the other shoot.

Controls:
1: Start button
2: Insert coin
Escape: Quit game

Arrow keys or WASD: Move ship
E, X, K or Enter: Bomb
Q, Z, J or Shift: Toggle movement speed (slow/fast)
Left click: Shoot (hold for focused shot)
Right click, Mouse wheel or Space: Toggle auto-targeting (on/off)

There's no key configuration option, but the keys are set up so multiple "control schemes" can be used.
 
One Player (left hand movement, right hand shooting)
WASD: Move ship
E: Bomb
Q: Toggle movement speed (slow/fast)
Left click: Shoot (hold for focused shot)
Right click, Mouse wheel or Space: Toggle auto-targeting (on/off)

One Player (left hand shooting, right hand movement)
Arrow keys: Move ship
Enter: Bomb
Shift: Toggle movement speed (slow/fast)
Left click: Shoot (hold for focused shot)
Right click, Mouse wheel or Space: Toggle auto-targeting (on/off)

Two Player (left hand movement, right hand speed/bomb controls)
Keyboard player:
WASD: Move ship
K: Bomb
J: Toggle movement speed (slow/fast)
Mouse player:
Left click: Shoot (hold for focused shot)
Right click or Mouse wheel: Toggle auto-targeting (on/off)

Two Player (left hand speed/bomb controls, right hand movement)
Keyboard player:
Arrow keys: Move ship
X: Bomb
Z: Toggle movement speed (slow/fast)
Mouse player:
Left click: Shoot (hold for focused shot)
Right click or Mouse wheel: Toggle auto-targeting (on/off)

Scoring and Rank:
This game has a "rank" system that is tied to scoring.
The higher your rank is, the more points you earn for destroying enemies and collecting jewels.
However, the game also gets harder as your rank gets higher.
Rank gradually increases over time, and it also increases when you shoot enemies, collect jewels and graze bullets.
Rank does not increase during boss battles.
Rank decreases when you activate auto-targeting, use a bomb, die, or continue after losing all your lives.

If you fly near the top of the screen, you will automatically draw jewels towards you.
Collecting jewels like this increases rank more quickly than collecting them normally.
Every time you collect 100 jewels, you earn an extra life and bomb.
There is a bonus at the end of the game for the number of lives and bombs you have remaining.

Gameplay Tips:
To get the "good ending", you have to complete the game without using any continues. Here are some tips.

If you just want to survive, and don't care about your score, it's best to keep your rank as low as possible.
Auto-targeting decreases rank, and is just generally very useful in a lot of places, so use it frequently.
Bombs also decrease rank, so you shouldn't conserve them too much.
Figure out which areas are difficult for you and use bombs liberally to get through them unscathed.

Collecting jewels gives you extra lives and bombs, but it also drives up the rank quickly.
You might actually find it easier to avoid shooting enemies and collecting jewels in some places so that you can stay at a low rank.
For example, if you try to shoot everything and grab lots of jewels in the first stage, you'll probably reach the boss at Rank 2.
But if you skip some jewels and avoid shooting certain groups of enemies, you can reach it at Rank 1, and it will be easier to deal with.

Make sure you're familiar with all the mechanics.
Large enemies are much faster to destroy with the focused shot (hold the left mouse button).
Also, many bullet patterns are a lot easier to dodge if you change your ship speed to slow.

I normally play with my dominant hand controlling shooting and my other hand controlling movement.
But for some areas, I switch to my dominant hand for movement and rely on auto-targeting for shooting, or just bomb past enemies.
In particular, this makes avoiding the walls and obstacles in the third stage much easier. It's also useful for bosses.
Of course, you could also try playing with a friend so you don't have to focus on shooting at all.