A few things, good and bad
You really need to either do one of two things: either make the ship smaller or make it move around the screen faster. I don't know how many times I've died simply because my bulky ship can't move itself out of the way of a flurry of bullets. Or just simply because an enemy rammed into me from off screen at a speed that was just impossible to dodge with the sluggish ship. Making yourself easy to hit doesn't add difficulty, it just makes the game frustrating and even brings some luck into it at times.
Another thing that needs to be addressed are the visibility of the bullets. They weren't hard to see when there were only, say, 7 enemies on the screen. But any more than that and they might as well be invisible. This problem is mainly just compounded with the ship's bulkiness/lack of speed. Also, the need to memorize patterns to make up for speed does not equate to difficulty.
Finally, the leveling system. Honestly, it felt like this shouldn't have even been here. There is no immediate benefit to leveling up since all of the "stat" increases are worthless and do not change the performance of your ship. You still move sluggishly, your weapons take around the same time to down enemies, you get hit basically as hard as before and you're still relying on a mod to boost your armor or weapons(the speed mod was worthless, really). Sure, it's noticeable after about 5 level ups, but by then you're just facing stronger variants of enemies so it cancels out immediately. And then there's the fact that it's literally impossible to grind for experience.
All that being said, the game definitely wasn't all that bad. The upgrade system was pretty good, since the weapons were pretty balanced. Music, as mentioned before, was a huge plus to the game as well. If you just polished up the game a little bit it would be great.