This is my absolute favorite genre, and I am so glad you made this game. My first impression of it is that it has great potental but is too unrefined to win over anyone but Master of Magic fans. Here is what I hope you find constructive feedback.
Good:
I love the fact that there is so much to this game. I feel like I am completely lost in the complexity of it all, which is very refressing considering how dumbed down modern games tend to be.
Neutral:
The concept of having to drag-click was a bit jarring at first but seems perfectly reasonable once you get used to it.
Bad:
It is really hard to deal with the inventory screen when I can't see what I have equipped and what I can buy at the same time.Perhaps you could take a look at the design and make it easier to upgrade my heroes.
How about letting us play with zero opponents, and letting us continue to play after we have won. Starcraft 2 and Sins of a Solar Empire let me do this. It is good to be able to mess around to learn some of the more advanced content. I just had an experience where I was trying to learn the game, so I choose only a single easy opponent. He got himself killed, and I won the game without having time to even figure it out. Very unsatisifying.
When looking at the character inventory screen, it would be nice to be able to switch characters.
I commonly need to select all units in a city and move them out. I find the way I have to do this very clunky, especially if there are a lot of units. Can we have a "select all" feature?