The control limits the creativity of the game. The controls are quite awkward at first. The only time you feel like you are in complete control is when you are locked on to an enemy. Other times are filled with slow turns and imprecise jumping. The combat can also get quite repetitive. Despite this negative talk, the game is still actually enjoyable in short bursts.
As far as I can tell from the rather stupid opening, you use a biological experiment called Maken that grows its own mind when infiltrating a body. You use different bodies and weapons for different missions. This process of going from body to body as Maken is called brainjacking, your skill at which is represented by your BJ Rank.
The point is, the control holds this game back from its full potential. I would love to see a sequel with better controls and the same zaniness that sets this game apart. The game is just bizarre and I recommend to somebody looking for a unique experience, but the game is not quite a must have for everybody's Dreamcast collection.