Fabricate is a problem. Its very existence is a monkey wrench in an already shaky game economy, and when PCs get it it can be easily abused to accumulate wealth of game-breaking proportions.
Detect Magic, as written, is a problem. It's also Detect Illusion, Detect Invisibility, and frequently Detect Enemy and Detect Trap. I'd like to limit it to the ability to sense magical effects on things in sight, but that's not how it's written.
Polymorph, Polymorph Any Object, Shape Change, and to a lesser extend Alter Self and a Druid's Wild Shape have tremendous potential, power that may well exceed their levels.
Gate has game-breaking potential: The ability to summon one or more Solars and/or Titans into a battle is a neat effect for a climactic battle. Not so neat when you begin seeing them all the time.
The Sand Storm spell, and to a lesser extend Control Winds, can be used as Slay Army or Slay City. Each contains the quite reasonable potential to create an F5 hurricane or tornado a quarter mile across, and just walk it through a city or armed force, leveling everything in your path. You can direct it to circle you constantly as you move, making it practically impossible for any opponent to stand within that quarter mile of you. Now, the spell does have a Save (Fortitude negates), but people in the area need to make that Save every round they're exposed to the wind and, as written, they're actually incapable of getting out of the stronger winds.
Stepping away from actual spells, the Diplomacy and Intimidate rules need serious work. They're not written as opposed checks, meaning that a well designed "Diplomancer" could theoretically talk a Balrog into joining a group of good heroes. To emphasize the ridiculous power of this, it's as easy to talk the Big Bad of any scene into being a fan and supporter as it is to do the same to the village idiot. I mention Intimidate because, aside from the duration of the effect, it uses the exact same rules and target numbers. One dice roll and the Big Bad is your best friend.