Reynard
aka Ian Eller
I've looked through the free preview.
Overall, it is very to understand.
How different (if at all) is the full version of the game from the free preview?
It's a huge amount of the game. It's only missing higher level spells and monsters. You could go up a few levels with this to find out if you like the game or not.
There are only 10 levels, and I think that this covers you up to about half way?
in addition, the full game includes a lot of extra tables and things, making it even easier to run on the fly.