The basic gameplay concept of Clash of Heroes is that each colored "gem" on your screen is actually a soldier in your fantasy army -- a unicorn, elfin archer, animated tree, or the like. Lining up three of them vertically commands them to "attack," in which case they charge forward after a few turns, destroying the enemy troops in front of them and depleting the HP of the opponent. Lining up three horizontally causes your troops to defend, literally turning into barriers. There are a few extra rules, but that's basically it.
In two-player (the only variant of multiplayer I tried -- I was unable to play the four-player competitive or the co-op mode), one player occupies the top half of the screen, the other player occupies the bottom half, and they let loose their mythical armies against one another. If you know how to play the DS game, you already know how to play in multiplayer! If you've already completed the game, you might find yourself able to compete with crazy fans online.
That's not to say that Capy is content dumping the DS game on XBLA and PSN. Though I was told all the animations weren't yet in place, the art has been completely redone, with new hand-drawn sprites for every single in-game character. The 16-bit look has been replaced with realistically proportioned, smoothly animated sprites on detailed, cartoon-style backgrounds. Capy has also gone back and rebalanced the entire game, changing, adding and removing abilities from the various units. The single example I saw -- Anwen's Sniper Shot -- replaces a single, super-damaging arrow shot across the screen with three less potent arrows, to prevent that attack from being overpowered.
Ubisoft plans to publish Clash of Heroes HD this summer. I look forward to being able to find people to play against, instead of vainly searching for other people nearby who have the DS version.