Great game, very addicting.
As already mentioned, there could be some indication of the base dmg dealt the abilities, as well as the dmg increase per grenade/bolt/meteor/etc you get by adding level points into ship damage.
Meteor rain and homing missiles need some improve, the dmg dealt by them is too low for the mana cost. The maximum mana is pretty low too, making grenade pretty much the only dmg skill worth using. I also missed some way to increase skill usefulness other than lvl pts. It would be nice to see some max mana or mana regen bonus in the items, and perhaps making ship dmg from equips also affect skill dmg.
The gold reward from the battles is also is very low, making the x2 gold bonus and the passive gold boost a little useless. My main source of income in the game was from selling loot. Even poor loot already gives a lot more gold than the battle reward. This makes the ??? section of treasure chests more rewarding than the 2x gold one, which doesn't make much sense. An advance button to skip the chest spin animation would be nice too.
Other than those minor issues, the game is pretty solid. Its challenging enough at some points, but totally beatable without spending money. The unlimited skill and lvl pts resets are nice for changing your build, when you need to beat an specific level, or grinding for a while with the bonus loot from the passives, to make money if you see a nice item in the shop. The free crystal supply in the game is very good too. Its not that hard to get the 3 crystals from chests, and you can fully upgrade an item with that.
I believe theres a bug with mega beam. If you die while the beam is on, it continues indefinitely after you respawn.