First up, great game so far! I'm having about 100 times more fun than I did with WoM. Great game in the works here, keep it up.

The biggest most obvious bug I've come across so far is the Firestorm spell. Whenever I use it on a city, the city disappears. And then, when I walked my Sovereign in to the now disappeared city to see if I can capture it, I get 5 death notifications in a row and then I cannot find my Sovereign any more.

It also doesn't work in the field... I once cast Firestorm on an enemy Sovereign. He and his army disappeared, and then one of his nearby cities disappeared off the map. This time the disappeared city leaves all the stationed troops exposed, and I fight them without any problems, but then with the army that fought in the disappeared city it seems like I get a bunch of free moves on the map. 

Very strange, very buggy spell right now. But it's so obvious you must have noticed it by now...