Extreme difficulty, but for what reason?
As a game, Sky Quest is enjoyable. However, the execution turns it into a chore. Levels are filled with bullet-spongy enemies who bounce around a time limit before executing an ultimate "You're screwed" finisher. This gives interesting variety; - You have to know what is the biggest threat, and when...But it can also make the game's slow start incredibly frustrating. It feels as if everything is geared towards you spending a dollar or two to get an upgrade, to get that "Little edge" over the game.
The RPG mechanics are fun, although the skill tree is drab and uninspired. There's room for improvement; - Possibly more enemies while lowering their maximum health, rather than everything a meat-shield that you have to pound bullets into, risking precious life.
I can give it a 4/5 since I truly enjoy challenges.