Very easy game to complete. This is a full guide with strategies to complete this quickly
I also included my own video with this guide.
Strategies
1. You know you're hitting what you're supposed to be hitting if sparks fly off of it.
2. On casual you are a bullet sponge. So just hit your target. Don't worry about dying.
3. When you destroy enemies you get power ups and health.
4. On level 4 when you get to the orange block wall. Just shoot at the block that sparks when hit.
5. You can just hold down the A button to rapid fire.
6. On level 8-3 just shoot the red bomb that keeps falling from the sky.
Combo 500 and Combo 1000 achievements
The best level to get this on is Level 6. When you get to the boss on this level. Stay on the bottom middle of the screen a inch from the bottom of the screen. Just shoot straight up at the barrier that's shields the red target on the boss. You will have black squares from both sides coming at you. When they touch you they'll paralyze you. Just keep shooting. When you destroy them they'll drop power ups, shields, and health. You will notice your multiplier going up on the side of the screen. At X500 and X1000 you will get your achievements. You can get this on your first playthrough of level six or come back through level select.
How to beat level boss 6
On the left and right of the barrier that shields the red target. There are 2 black squares buttons you need to destroy. This will temporary remove the barrier over the red target so you can shoot it. The square buttons spawn black squares that come at you. Shoot the squares to get power ups, shields, and health. Keep repeating the process to defeat the boss and level 6.
Just beat every campaign level on Casual.
To get all other achievement.