Meh. Bought this for $1.50 so I can't really complain. It's an old school side scroller with old school design. It other words, it's a controller thrower...
It gets very repetitive, has no map despite a maze-like ship, has a terrible animation when you get hit that causes major problems later, and has a boring storyline whose sole twist you'll see coming from the start.
The difficulty can be adjusted, but in game it's pretty simple until the final part of the story. All of a sudden the difficulty is ramped WAY up. Instead of 4-5 opponents on screen, you've fighting 20 or more at once. Also, instead of the one hit kills you fought en masse earlier, these opponents take several shots to kill. Don't worry though, you get more powerful weapons along the way in the story, BUT in this phase they're very, very limited to what you brought and the crappy shotgun. Expect to run out of ammo before you clear the first room, and there are three of these... What makes it worse is that crappy "I got hit" animation that causes you to effectively get stuck in your enemies if you make the slightest mistake while moving non-stop during this phase. I can't say this is "old school design", just a huge design mistake.
Once you get past this area you get to fight a boss that you must grind down slowly. No easy trick to beat it and it'll take a few attempts for you to get the pattern down.
I won't say this game is completely awful, but it's not great. There are better games to be played on Steam unless you really long for the old side scroller days (in which case, have at it).