I don't know what the problem is with the people who only gave this toy one star. It's not the easiest thing to put together, but once you do it and do it properly, its a total blast. For the woman who says she's not sure it doesn't work because she lives above 6,000 feet...the directions tell explicitly you how to accomodate for high altitude. They also say you need to fill it with pure helium, not diluted helium, so I made sure the party store where I got it filled had pure helium. As I'm writing this I'm watching my son navigate this thing around the room, it's hilarious to have a huge shark (like over three and a half feet long) swimming around my house. the tail goes back and forth via remote control to make it "swim," and there is a battery-operated counterweight that goes back and forth under the shark's belly to dip the shark's nose up or down to make it change direction. There is a compartment within the motor device in which you put pieces of clay (weird, but it works), or remove them, this will either weigh the shark down so it doesn't float too high, or remove a piece or two so it doesn't sink too low. It's just a matter of fine-tuning it, reading the directions and putting it together properly. I always read the reviews of the people who only give one star to an item in which I'm interested; if they can't spell, have lousy grammar and/or whine about the fact that something is too difficult to put together or make stupid comments over obvious necessities about the product (like the fact that you stick the fins on with double-sided tape...hello, why is that a problem? How else do you suggest you get the fin to stick to a balloon...)Comments like that let me know that their one-star rating is more about their inability to put something together rather than the actual item itself.