Heroes 6 - Discussion

It depends on which template you choose. The maps may not always be perfect, but they are quite playable. There are a couple of good templates in Heroes of Might and Magic V, and you can also find some in Heroes of Might and Magic III. As for scenarios, most of them are designed for single-player. In my opinion, it's better to play random maps in multiplayer.

Added after 3 minutes
And yes, it's very easy and, most importantly, quick to create a map for duels and mass duels.