Good game but...
This is a good game but there a few serious problems that let the game down.
The first problem:
Too much False Difficulty... that isn't to say this game is difficult (it's not) but that what difficulty it does have comes from poor game design and not challenging levels.
The vast majority of the difficulty in this game is:
Not having a clear sense of your ship's hitbox. I saw a single version of the ship with a white dot in the middle but it seemed clear that that wasn't the true hitbox. Without an obvious true hitbox you're flying in the dark and it makes the game a lot more difficult, but not in a good way... in a frustrating and unfun way.
The other half of the difficulty in this game is:
Not having a clear sense of the bullet hitboxes, ESPECIALLY the laser ones. The hardest map on this game was the one where lasers were spammed at you. The rest of them were extremely easy.
The second problem:
It's too easy. For anyone who ever plays Shmups this game is a joke IN SPITE of the false difficulty from the hitbox issues. I beat this game without using time slow at all.
Why the game is easy:
1) Your ship has multiple HP.
The ship shouldn't have multiple HP, the fact that it did allowed me to beat the game without ever using time slow because mistakes didn't matter. If I did use time warp the game would not have been challenging at all. However, due to the false difficulty from the hitbox issues HP is pretty much required for non-shmup players else they'd kill themselves in frustration. The solution is simple, fix the hitbox issues THEN remove HP.
2) Time slow lasts too long.
Time slow isn't a bad 'save your ass' mechanic for shmups, but in this the time slow is just way too long, upgraded or not.
3) Your ship gets upgraded permenantly.
There is essentially no detriment to dying, especially because you can retry stages (more on that later). So upgrades just make the game easier and easier. The upgrade choices are also completely meaningless, since there is ultimately no sacrifice in what you get (you can't choose to prefer attacking over defense, you just end up getting everything). Not only that but it mucks up the difficulty progression (more on that later too).
4) Retrying Levels with any sort of 'save your ass' (time slow), lives, or hit point mechanic makes any shmup easy. You have all three.
It's not just you, SO many people who make Shmup games on Newgrounds miss that the difficulty from shmups is their ability to wage a war of attrition against your resources. By splitting up the stages and letting you retry them over and over you remove any true difficulty created by having to get through all X stages with Y lives/bombs/etc. There are no such concerns in this game.
5) Giving me even more upgrades for the last boss... an encounter of which is only as difficult as the most difficult boss it turns into, all of which were bosses I've already defeated... Did I mention the false difficulty created by the boss randomly switching between forms and having a hitbox on its body (you can never know which it'll turn into and thus it could literally spawn on top of you) yet?
The Third Problem:
The difficulty progression is completely mucked up, partially because of the hitbox issues (laser spam stage is false difficult, rest are easy) and partially because of the upgrades (the harder levels don't get hard enough quick enough. Upgrades make the later levels easier than the starting levels).
The Fourth problem:
Not enough variety. You have two bullet types, round bullets of various sizes and lasers of various sizes. The final boss was terribly designed and just lazy on your part. The music, while good, was ultimately just repeated stage after stage. The choices presented in game were meaningless, make them meaningful or scrap the choices all together. Randomly adding stuff a game doesn't make it better, it needs a reason.
That being said... The game is ultimately pretty fun (when you're not being frustrated by false difficulty). Good music, good graphics, groovy concept. Except for the above problems: Good game.