RTF is a global modification that replaces all towns in the game.

If any interesting-looking mages appear, send me a screenshot or just describe them; I'm curious about what canonical characters exist in the free cities.

Okay, agreed. In general, all opponents encountered are recorded in a bestiary, and you can always view them, replay their animations, etc. Also, the lore is interestingly revealed in the books you find during the game. By the way, the game is mostly filled with units from Dark Messiah, Heroes 5, and Heroes 6, and as I understand it, the developers didn't bother creating new models but simply transferred them to M&M10.
As for new content, they interestingly presented the Elves: the elven women, as I understand, have completely new models, while the male elves are a recolored and slightly edited model of Raileigh from Heroes 6.