The basics are what you'd expect—build decks of heroes, spells, and items, select your cards, and do mana-fueled battle on a colorful, pyrotechnic game board—but it looks to be every bit as complicated as it sounded in our recent preview: A hero and "creeps" in each of three lanes do battle sequentially, after which a "shopping phase," where gold earned from kills can be spent on item cards, takes place.
Once that's wrapped up, follow-on heroes are deployed: The first three heroes are placed automatically, but reinforcements can be placed wherever you want them. The process then begins again, until two of your enemy's three towers are destroyed, and victory is yours. (Or the other way around, as the case may be.)
There's a lot more to it than that, and it will take a more experienced digital cardsmith than I to fully analyze and explain what's in store. Fortunately, our man in Seattle—that's James—will be taking a closer look at it himself very soon.