The great thing about this game is how it builds the challenge as you play. On the first run it gradually introduces new enemies and obstacles that never feel unfair, but constantly force you to use your limited set of movement and shooting to contend with them. Once you run through the stages once, the challenge mode adds a few more variables on the first run before getting progressively tougher. There's also some neat graphical touches like how your vehicle drives through explosions from the saucer bombs when you just barely avoid them. The backgrounds do a good job of being unobtrusive while providing a good sense of traversal, but I do wish there was more here than just the tiles of the city and barren landscape.