Was this really made in only a month? Doesn't seem like much time to create the next Geometry Wars, but that's exactly what they've done.
A note on upgrades: you assign each upgrade to ONE level; choose the level, then choose the upgrade BEFORE clicking "enter sector"; later, beat the level again without using the upgrade to get the upgrade back.
A great thing to do when you're stuck is go back to earlier levels and beat them again without the upgrades to free those upgrades up again.