Populating the game are mutated version of recognisable animals and even the player's choice of ship is limited to things that look like they're held together by vine and bone as well as wire and bolt. "Think of it as David Cronenberg's 'R-Type' and you'll be within spitting distance of understanding what the flipping crikey is going on" EuroGamer once said.
As the pilot of one of four bio-ships the player is responsible for finding a new home for the survivors, while destroying all biological contamination that you happen to come across. It's an original, if not particularly deep premise, but it is enough to serve the purpose in a shoot ‘em up. After all, this is a genre where you need only an excuse to blow away the thousands of enemies that stand in your way. Staying true to the narrative most stages take place in natural locations such as jungles, caves and even the ocean. Other stages see the player flying through the ruins of former cities and abandoned research facilities, twisted and deformed by the rampant vegetation. However, despite its unusual premise 'Bio Hazard Battle' still manages to include the staples fans of the genre have come to expect. There is the requisite battleship stage where the player has to take out a remnant bio weapon piece by piece. Although all organic in design, every stage introduces something new; typically an enemy or environmental gimmick.
The enemies in the stages however, are consistently interesting and at times repulsive. They are "squishy and odd, undulating through the sky towards you in a freaky manner" agrees critic Simon Parkin. "You'll be up against some of the nastiest, most vile creatures you've ever seen. Things like mega amoebas, nuclear crabs, electro worms, and gut-grabbing insects" claimed Mean Machines magazine at the time.
I'm of the opinion that games should support you when you're struggling, not make the experience harder for a failing player. This isn't the only time when the game suddenly gets excessively difficult though.