I think this completely depends on who you are playings.

With Paradin, 100 : 100 ratio is easy money.

For the record, I think shrink is great as is, great way to deal with high-attack enemies (shrink them then kill them last), and Life magic NEEDS a spell like this. 

1. Candlecloak. Costs a lot, does very little damage and does not scale. Increase the base damage and add +2 per fire shard.

2. Celerity. High mana cost and requires a lot of air magic upgrades for only +1 initiative.

3. Chaos. Slow is just much better.

4. Shockwave. It requires putting my hero in harms way and does very little damage. Thunderstrike is weak for the same reason, as is Riptide. These spells do the same damage as burning hands but are much higher level.

5. Propaganda, if it is indeed set at only +1 gold per essence. The amount of gold is already very low at +2 because we only get the portion according to our tax rate!

6. All summoning spells in the summoner tree after Air Elementals. I would like to use these, but it takes a lot of traits and the summons are weak or slow.

7. Bless City and Curse City. Huge mana cost!

8. Destiny's Insight. Too costly. Even if mana cost was decreased to 1000, it would mostly be useful for one cast per newbie hero to help with leveling.

9. Stoneskin. Could scale better, make it +2 per earth shard?

10. Curgen''s volcano. Still looks useless even after the changes in the patch notes. Compare to spell of making cost, 500 mana, Curgen's volcano is much more difficult to pull off. Yet it only kills one city. It is typically much better to conquer the city... honestly one of the early battle reports where Frogboy won the game by spamming Curgen's Volcano was pretty cool. The mana cost could be like 300-500 mana, and reduce the casting cost to 5 turns. Also, increase the cost of the Spell of making to 1000 mana so Curgen's Volcano looks better in comparison.

6. Gust of Wind - A much worse version of Titan's Breath. Add some cold damage.

For the record, I use Counterspell... but I get really pissed when it doesn't work (gets resisted).  I think if we're going to waste a turn casting Counterspell then it should work.  Or could get rid of it and encourage the use of Spell Leech and Feedback instead (make them more desirable to cast)... at least there's an extra reward with those spells besides just countering the spell.

I agree with most of the other suggestions here about the spells. In general, I feel that most of the summoning spells are overpriced at the moment.

This is a great idea! It would make leveling up the spell schools a lot more tempting. Currently I always find myself going for the class-specific traits first with my sovereign because those take so long to level up. I will only level up magic to the max at the end of the game.

If I remember correctly, back in FE a trait in a spell school could often give three spells, so for example by leveling up earth magic one could get the "sunder" spell if one also had fire magic. But now that these spells have been moved to the mage tree, the spell schools need a buff.

I disagree with the folks who want counter spell removed.  In early game, facing a (the ethereal thingy that 'wails/ can't be hit with non-magical weapons) - counter spelling is only way for low level stack to have any chance of success. 

I don't think that they want counterspell removed, I think that they want it changed so that it has some utility against the predominantly instant-cast spells that Legendary Heroes has.

For example, by making it a curse-type spell, where you cast it on a target and if it sticks, then the next spell that that target attempts to cast fails, or a defensive spell that you can cast to give the next hostile spell cast at your army a chance to fail.

I'd personally rather see the spell-granting traits in the summoning line become something like Shrill/<Intermediate Elemental-type units>/Elemental Mastery and perhaps a couple others, granting you the ability to summon Shrills of various elements, Ignys/Ophidians/etc, Fire/Ice/Air/Earth Elementals, and then have a few specialist traits branched off letting you get special things like Summon Delin or an ability to summon a Shrill Lord. Even better would be if the spells you received at each level were determined by what spellbooks you had - no more water/air mages with Fire Elementals, or things like that.

As for spells I think are currently not useful:

1. Shadow Bolt - either I can make a spell stick without this, or I'm not really high enough of a level for this to help that much anyways.

2. Counterspell - most of the spells don't have a cast time anymore, despite that they are often as strong as those that do have casting times.

3. Blind - -25% accuracy isn't much of anything. The dodge reduction in the patch notes for 0.92 might be decent, but once I get a fortress up and running or have a decent commander hero, dodge isn't really a problem for me anymore.

4. Candlecloak - I've never seen this do more than maybe one or two damage to an attacking unit, and it costs a lot to cast, so I don't really know why I should bother using it.

5. Death Lash - I know it's meant to be used on slave units which are extremely expendable, but even on them it's questionable - much beyond the early game, slave units are hardly worthwhile except as fodder, and in the early game it isn't really that good of an idea to continually have to replace parts of your army because it slows down city development (Slave Militia may only take one turn to produce, but 1 turn times however many you sacrifice for the relatively minor bonus conferred by this? I'm pretty sure that in most cases I'm better off casting Cull the Weak and then Flame Dart, if I actually want to get anything done).

If I can think of more, I'll add them later.

Huh, how did I miss this thread?

Giant Form? Its a good spell at 30 mana to double your attack with no cooldown, but I feel that it fails as a lv 5 Earth spell. It would be more fun if it cost around 60 mana and added a health bonus as well. Its seems very strange that the ultimate tactical earth spell that 10x your size adds no health. Would be awesome if a giant form champion had the same booming steps as the Pyre of Man, hey are the same size afterall. You could even take it further and at 90 mana, also adds 50% splash damage.

Pandemonium and Chaos. Both terrible spells that aren't worth casting.

Summon Ice Elemental and Ignys. Weak Summons you are forced to take, would only summon if the only summons you have.  Add some buffs to summons and allow groups of weaker summons (Ignys, Ice) later game to make older spells relevant again.  Please redo summoners tree to make based on elemental traits and multiple summons per summoners trait. Also why no summoning Shrills? 

Crusade: A decent spell but never use it as level 5 spells are so hard to get and others are much better as they just straight up kill armies and cities.

Celerity: Same problem as Crusade. Not sure this spell can be fixed.

True this. Now that we get all these Mancy traits and there are no dual element spells, its not worth it to invest in an elemental trait when you can pick up decent spells for 1 trait point and advance up the tree. If you have ridiculous mana you can get the game ending spells like Tornado, Earthquake and Ventairs Howl, but otherwise not worth it.