Lou: Yep - I love MM - Just saw they have a new MM for the DS - will have to keep this on the radar until the price drops - heard anything about it?
Like Thiev said, it has more in common with puzzle games than with the rest of the Might and Magic series. The story and characters come from Heroes of Might and Magic V's story, but it isn't necessary to have played that game's campaign to appreciate the story.
That being said, I found Clash of Heroes extremely fun and rewarding. The battle system is clever and exciting, one of the few battle systems that can make even the most mundane fight fun. The story is nothing spectacular but it manages to keep your interest throughout. You may or may not be turned off by the game's anime presentation, but it really isn't too distracting, and this is coming from a huge anime anti-fan (I just don't get it.)
Don't get the game if you're looking for MMX, as it is a completely different experience from the RPGs of the series, as well as from the Heroes games. However, it is amazingly fun in its own right. If you don't trust me, check out the reviews: it got surprisingly great reviews across the board from most of the reputable sources.
I can't encourage this game enough, though! It was a really fun experience.