I recently bought this as I'd been looking for something to play when I only have a few minutes and don't have time for a more in-depth game. The closest I can compare it to is Sympthony. In both games, the songs you pick to play are used to design the level and opposition. In Beat Hazard 2, though, the power of your weaponry will also be affected by the pace/beat/tempo/etc. of the music. In addition, you also get multiple ships to potentially buy and customize, which gives more variety and reason to keep playing. And, yes, as noted elsewhere, this is not a bullet hell game but rather a two stick shooter.
Unlike Symphony, however, there's not even a thin pretense at a story or plot. You pick a track, start a run, and shoot at things 'til you finish or run out of lives. In some of the areas, however, the visuals get so intense and distracting it's almost impossible to keep track of what's around you or coming at you, making it little more than dumb luck to either survive or die. That and the fact that some of the ships that are made available are very clunky and difficult to fly, not to mention the lack of a tutorial, cost the game a star.
If you're looking for something simple, quick and fun, this is a solid choice. If you're looking for any kind of character or storyline or plot, look somewhere else.