In the late game there are a couple spells that need some work.  Earthquake and Curgen's Inferno are both super powerful.  In fact Curgen's Inferno can wipe out an entire city in the blink of an eye.

I am fine with the power, but my suggestion is these two spells need to have some type of casting time and be within a certain range to cast them.  That way if you see an enemy channeler conjuring and glowing within range of your city you have a chance to act on it.  It did not happen to me but I took out an entire kingdom just by casting those two spells.  These two spells are brutally powerful.  Very cool, but very powerful.

Besides, I think it would be cool just seeing the channeler building power to cast the spells.

My suggestion:

The channeler needs to be within the aoe, as the channeler builds up the power you could have some special effects drawing towards them.  Then if they are interrupted the spell is broken.  It would be even better if the channeler goes to the tactical screen and you have to get them or prevent them (depending on what side you are on) from moving or taking any damage.

Curgen's inferno--4 seasons

earthquake--2 seasons