Your ship moves left and right at the bottom of the screen, and fires up at your opponent, or opponents. You and your opponents have a shield which needs to be worn down in order to continue, so it's necessary to time your fire such that your shots both get through obstacles in the center of the screen, hit the opponent aimed at AND don't leave you exposed to return fire.
After a number of various one on one levels with differing conditions, there'll be a boss stage (for example, the first 'boss' screen is three ships moving left and right that you have to wear down while dodging their own shots and shooting around obstacles in the way) and then selecting a new planet (I.e. set of levels).
While it might initially seem a bit simplistic, the game does add an increasing amount of wrinkles to the concept to keep things exciting - one stage has the obstacles in the center of the screen movable by shots, so that it's possible to trap or be trapped in part of the screen. Also, occasional power-ups such as shield increases, stopping time and increased fire rates can be helpful in a pinch.
The graphics aren't particularly stellar, but the overall presentation is nice, and it's easy to keep track of what's going on around you in the game. Sound? Yeah, it has some. Notice how underwhelmed I am?
Personally, I found that it's straightforward to get to a second planet, but once that milestone's been achieved, the difficulty level starts to ramp up. It's not instantly impossible by any means, but should provide a longer term challenge. The game does have a two-player link mode, but I've had no opportunity to try it, and can't comment, unfortunately.
Overall, you could easily find worse games than this in the Game Boy library. You'll undoubtedly find Volley Fire to be a fun game, at least in small doses. Don't expect much from it long term and you'll be fine.
