One of the best Flash games of its genre
There are _lots_ of games, even Flash games, of the vertical shooter genre. Particularly good members of the series stand out for certain reasons. This one's reasons are the following:
Difficulty level = somewhat challenging yet not unplayably hard. Personally I'd prefer it to be significantly more difficult, but I tend to be pretty good at this type of game, so it's probably fine where it is to avoid alienating most people.
Customization = sufficient yet not overwhelming. There's a sufficient amount of variety in the upgrade options to allow for multiple styles of play, and the prices are all pretty much balanced.
Pacing = perfect. Levels are exactly the right length to keep you entertained for a length of time and give you a break just when you need it, and level replays are handled precisely how I'd do it: you can only earn a limited total amount of money per level, and you only improve your score up to that amount, rather than replaying levels infinitely for infinite resource gains.
Sound = good. Good music, good sound effects, but I'd really like volume controls rather than just an "On/Off" toggle. It's a bit loud as-is for my taste; I'd drop it to about 70% of where it currently is if there were volume controls.
Unquantifiable fun factor = great. Enemy attack patterns, asteroid mechanics, control responsiveness, everything adds up to an unquantifiable fun factor that makes this game one of the best of its genre, right up there with Danmaku Legend II.
There really isn't really much else to say other than "Congrats, and please add volume controls."