It's a competent but derivative title that is almost identical to King's Bounty.
The game is basically the same as king's bounty. You have some Avatar that runs around the map, when you encounter enemies a little turn based grid pops up, and "Stacks" of various units can be used in turn based fashion against stacks of an enemy army.
Look at these two game play videos back to back... it's the same thing:
http://www.youtube.com/watch?v=16cYAo8NypI
http://www.youtube.com/watch?v=twIXp_ptS2g
And the sad thing is that I think King's bounty does it better. I won't claim that this is a comprehensive review. It isn't because I couldn't be bothered to look into it further. But the first big difference that is annoying is that you have turns on the campaign map. You can only move so far before you have to stop, click on the next turn button, and then you can move again. They did this because they didn't want the strategy map to be static like it is in king's bounty. If you ignore an enemy for 10,000 years in king's bounty they'll still be waiting for you no different hen if you had hit them 10,000 years ago. But in MM VI they get stronger as time goes by so if you ignore them bad things happen. That sounds neat but it doesn't really add anything to the gameplay and it's more annoying on the campaign map then anything.
I'll stress, this isn't a bad game. It's well made, the art is great, the engine looks solid, but the gameplay is highly derivative and better done elsewhere. I expected more from this franchise then a king's bounty clone.