Magic needs a catch. The reason it isn't engaging so far is that it's the same ol' same ol'. There's nothing new about it. Probably, Frogboy feels that it's wrong because he's hailed Elemental as the next 'big thing', so to speak.
So, here's an idea that just now came to me. It may be doable, it may not be doable. I figured it's worth saying, at least.
Thus far, magic seems to be, easily, the salvation and/or damnation of the world. It's a bit of a missing factor - the energies of magic are not wholly part of the world. Whenever you cast spells, then, you bring those energies back into the world. Sometimes, the energies linger - for better or for worse.
Each spell you cast leaves behind some traces of its type. Casting spells of a fire book leaves fire traces, water leaves water, summoning leaves summoning, etc. Each book stands against another, so that their traces neutralize each other. So equal numbers of fire and water traces would flat out to zero.
More traces are left with the more spells you cast. This buildup becomes a great font of power - as you cast a bunch of fire spells, there is so much fire energy in the air you can cast spells for free (by draining the traces instead of using mana) or have spells that are simply more powerful (a fireball with a lot of fire energy packs a hell of a punch, compared to a fireball with no traces of energy of any sort). Some spells have such a horrendously high mana cast that they will require you to burn through a lot of energy in the area to cast.
Eventually, there would be so great a buildup of certain energies (air, fire, etc.) that your area of influence becomes a certain domain. This domain gives passive boosts to units, and certain units and magical beings will be drawn to your territory (IE, having a domain of air would attract flying creatures. Of earth, sand golem-type creatures). The energies become so rampant, so powerful, that their influence causes occurences aligned with their books. Air domains will create sporadic storms, which will impede enemies and strike them with lightning. Fire domains burn enemies and penalize defense. A summoning domain randomly creates very weak units, powerful only en masse.
Thus, magic isn't the same as 'everyone is the same person with the same spells'. You get to choose which books to use, which magic to populate your kingdom with. Do you focus on just a few sorts of magic? You'll be far more powerful in them than others, but you will only be able to draw power from those particular types. Or do you not care about having the domain, instead wanting to be able to hurl every single spell in the game?
Do you choose power through variety and adaptation? Or do you limit yourself to just a few particulars? Be a battlemage whose magic is focused solely on destruction, or be a summoner whose very breath binds magic into minions? Or be a little bit of everything, jack of all books but master of none? The choice is yours.