Took a bit more time to test the game.
From level 3 (dynamite level) onwards it becomes quite challenging and therefore interesting.
I won't spoil the interesting parts but be ready to restart some levels a few times because there are some deadly mistakes that anyone is likely to do the first time.
One thing I noticed and that you can be wondering about the first time you find them: Extra weapons (flame grenades, arc gun, missiles/bombs for the ship) are not carried from one mission to another so don't hesitate to use them in the level you get them.
While you will be at it, I forgot to note the code for level 5 (and not ready to do level 4 once again), therefore, if you don't mind noting and posting it there, we could start to compile a list of level codes.
Here are those I have noted so far:
Also, be warned that some areas are a bit difficult: bunch of enemies shooting at you at the same time (and the game rom header is 'Rescue Game which is NOT a shoot-em-up'
) and two rows of harmful moving spikes you are supposed to fly through (in level 5).
I try to play the levels without save states but I had to use a few saves/reloads for these passages.