It's like that flash game those kids are obsessed with, Helicopter Game, though that's not necessarily a good thing.
Turn offs were the music, enemies, and lack of continues. Music is the same, no matter if I kill an enemy, sit at the main menu, crash into a building, or regular flying. There's no oomph to it, and flying a helicopter in a dogfight is supposed to be badass. The enemy vehicles were constantly repeated, just being a bomber or an enemy heli or some sort of jet. But the main killer was whenever I died, I had to do the whole. Thing. OVER. Say I got 5 levels in. I crash into a building by accident. I'm stuck all the bloody way back at the first level with 0 upgrades. Screw playing it again.
Turn ons were limited ammo and timer, allowing a challenge to the scenario and a sense of urgency, but still giving us chances to get speed ups, gain money, replenish our ammo stock, and the wonderful ability of a shield to negate those bombs dropping on our precious rotors. A game isn't a game without a challenge, and a game still isn't a game without the chance to make it somewhat easier on yourself.
Overall, it was worth a play and about ten to fifteen minutes of my time. I would play more if there was a damned continue button, though. That really killed the replay value of this game.