Whether it's the incredibly cute graphics, or the great amount of strategy needed to play it, its definitely addictive.
This game is somewhat difficult, but with patience, and plenty of practice, you'll definitely get the hang of it. It's a turn-based game, and its all about perfecting shots on the opponent(s). There are tons of different mobiles to choose from, ranging from the difficult Boomer and Kalssidon to the incredibly queer J Frog. After an hour or so, you'll probably figure out which of the bots is best suited for you.
What makes it difficult is getting shots to hit, while balancing your angle, power, and judging it based on the direction and velocity of the wind. You really have to be paying attention when you're playing this, or you'll mess up all your shots.
The only thing about it that turned me down was the fact that avatar items aren't permanent. The default time you can have one is a week, or you can pay extra to have it for a year, 5 or 6 times more the price to make it limitless. The system is really stupid. At least the fun makes up for it.
Not much else to say, but its a free game-- download it! You've got nothing to lose, even if you think it's terrible! I don't play gunbound anymore (since i have plenty of other games now) But i'm sure plenty of people out there (especially if you're into anime-style cute graphics) will definitely be intrigued by this game for quite a while.