I'd like to offer my feedback on the magic in the current beta. I will discuss magic from a perspective that includes difficulty, and assume that I am playing on Ridiculous. Obviously, everything I present here will be my own opinion.
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First off, nearly all tactical spells are 100% useless, and I never use most of them. No damage spell does even close to enough damage to be viable. Let's say mid-game I encounter enemy units that have 800-1600 health. No damage spell comes even close to scratching that. In addition, it is near suicide to place champion talents in leveling up intelligence - it is the worst stat in the game, BECAUSE magic is so useless in tactical combat.
The only spells that I consider useful in tactical combat are Greater haste, pull of the earth, rockslide, greater grip of winter. Greater Haste is insanely good, but requires level 4 spells and takes ages to research - still, once you get there it's worth it. Pull of the Earth - your bread and butter disabler. Not only does the enemy get to attack less, but they also get fewer counter-attacks, the most important factor to consider in ridiculous tactical combat. Rockslide, the use is obvious and great. You'll need to build a barrier of troops around your caster if you want it to survive, because there's no way you can kill the enemy before they get to you. Rockslide helps fill in the gaps. Greater Grip of Winter, level 5, the game is almost always over before you get there, but if you do it's the best spell in the game. A huge intelligence requirement means you'll only be casting it with your sovereign.
Moving on to strategic.
Fertility is great - on huge maps you'll have loads of cities and that means very low prestige in them. Your supercities will need the boost to get to level 5, if you don't use charisma heroes (you should). Obviously the maintenance cost is large, but this is for focused use, not extended use.
Revive Land/Desecrate Land - Great when your enemy isn't in his cities. Very situational, but obviously worth it when push comes to shove.
Call to Arms - This, and teleport, will save your life a hundred times over before the game is done. City in danger? Put a raid on training, cast this, you're golden. Call to Arms and Teleport are probably 90% of all spells I cast.
Nature's Bounty - You'll be begging for the extra food to get your cities to level 5.
Enchanted Hammers - Makes level 5 cities useful, helping you avoid those 25+ season building times. Couple with other similar bonuses for great justice. Wish there was a spell that reduced training time like this.
Call of the Titans - I never get to use it. Not sure why. Teleport is much cheaper, and the border to the enemy is always just a few tiles from his city.
Tornado, Curgen's Inferno, Earthquake - all good, if you can actually get to use them.
Sacrifice - Great use.
Stone Skin - One of the best spells in the game, a tiny amount of extra armor can make your unit go from getting 2-3 damage every hit to almost never getting hit. Extremely desirable early game when your enemy has five times the health you do, and the same gear.
All the summon spells are way too weak to stand up to enemies. Regeneration and Glyph of Life are very poor, no scale. There's a bunch of enchants that give +1 of something like materials or tech research. Also useless.
To sum up, there's a lot of good ideas, and obviously I can't expect every spell to be useful in every situation. But right now, the majority of spells lack any purpose other than to fill out the spellbook. Some spells need to be hit HARD with the nerf bat (teleport, call to arms). Other spells need a lot of love, especially summons and damage spells. Then you can get the AI to start using them, and the game will be a lot more "war of magic" than it is now.
In particular, I feel that tactical spells are extremely weak.
