Collect all the crystals in each level. Various gameplay elements keep things interesting, such as low gravity, reverse gravity, and various other powerups. Be careful not to accidentally shoot each level's air pressurisation equipment or the pressure will drop so dramatically that you'll swell up and burst!
you regain life every 10.000 score on normal, 5.000 on easy and 15.000 on hard (maximum lives/hearts you can carry at one time is 4) also radioactive...