After much searching, I finally found what is probably the most succinct explanation, which I have copied and pasted below. I have had it sitting in my drafts forever because Noah didn't have enough pieces to play. Thanks to the generosity of several people this birthday, he now has enough and I imagine as soon as I read thee rules to him, he will not want to play anything else.
Why am, I publishing them, you may ask?
Simple. As a help to other moms out there who are as clueless about this craze as I was.
MODERN DAY GAME OF MARBLES The Bakugan-Mania is here. I had no idea what my daughter was talking about since she spoke a mile-a-minute about what the latest craze in children's toys. These items are in extremely high demand and are similar in genre to Pokemon cards, Yu-Gi-Yo, and Digimon. The characters appear to be a spin off from Japanese anime, in my perception. What are Bakugan? They are action figures that are morphed from small plastic marbles, based upon a television show on the Cartoon Network. Each figure comes with a metallic card that has a point value. A point value is also imprinted on the figure. A magnetic lock in the toy is triggered to open when the figure is placed onto a metallic game card. How do you play the game? Each player starts out with 3 Bakugan and 3 cards. Only one care can be a special ability card. The youngest player starts. Depending upon how many players are participating (2-4), determines where the cards are placed in the arena. When a Bakugan is rolled and lands on a card, it opens. If the Bakugan does not open, the player loses a turn. If 2 figures land on the same card, a point total is taken to count up the power value of the Bakugan + the value of the card. The higher sum wins the card and the figure. At the end of the round, the highest total of points wins the game. My daughter's after-school care has an Bakugan Class where children play in the afternoon. She is 7 years old but her friends who have it range from 6 to 10 years old. This game represents a unique and revolutionary spin on the game of playing marbles. It is quite creative and superficially complex to play. However, many children are compelled to play it all over the country. Educational value Strangely, enough, this toy has an ACTUAL educational value by requiring the players to add up or subtract the values of each figure/card. Safety and Caveats Since these are essentially small marbles, caution should be exercised if you child has small siblings who may try to swallow this toy. It is too big to fit into someone's ear or nose; however the danger is accidentally swallowing it or aspiration (going into the child's airway). You should also be aware if you have pets since it may lead to a dangerous bowel obstruction if ingested/eaten by your pet. Durability These are relatively fragile items that require users to be careful with the moving parts. Sometimes, the mechanisms are defected or through wear and tear may not allow the action figure to open or close. Conclusion This toy system is, for now, one of the hottest items in the toy world. If you are actually lucky enough to find it, or willing to pay the premium, then you should strongly consider getting it. Your child will be extremely happy.