Fun. The game is quite fun, with lots of different planes, different helpers, but the stages, even trying hard to feel different, get repetitive and boring. So grinding for gold to level up your ships gets pretty boring pretty fast. There is a co-op multiplayer feature, but the other player doesn't actually play with you, he is a ghost playing the same stage. Difficulty is mostly about if you can do enough dps to kill enemies, since the levels to be hard just put enemies with a lot HP and almost nothing else. Graphics are fine for this kind of game, the music is good and the sound effects are decent. Overall it's a decent game.