When I was looking up some higher level sleep-inducing enchantments for the Lyre of Awakening, I naturally looked in Greyhawk and was reminded of how strongly I feel about the Greyhawk spell levels being incorrect. I've mentioned before that I feel Magic Missile seems like it should be higher than 1st level, but it's not just spell levels that seem too low; a number of the new spells seem like their spell levels are too high. For example: the Men & Magic 6th level spell list includes spells that cause large-scale effects, like Move Earth and Control Weather. There are even a few wide-scale spells at lower levels, like Massmorph and Hallucinatory Terrain. But several new Greyhawk spells with large-scale effects are at much higher spell levels (7th or higher,) even those these spells don't really seem more powerful than the original 6th level spells.
Reverse Gravity: Just a faster, area-effect version of Levitation (2nd level,) really. I think I'd drop this to 5th level, where Telekinesis is.
Phase Door: Passwall that's invisible. Make it 6th level instead of 7th.
Charm Plants: You have Plant Growth at 4th level; I really can't see putting this spell higher than 5th.
Mass Invisibility: You can turn an army into trees to hide them at 4th level. At best, this is a 5th level spell.
Mass Charm: Got to be 5th or 6th level at the most, instead of 8th.
Some of the others I'm less sure about, but I could see lowering Delayed Blast Fireball to 4th level and Meteor Swarm to no higher than 6th level. Some spells, like Simulacrum, Clone, and the Power Words may work better as rituals, with each casting as a unique one-shot spell that the caster must research. Others, like Gate, depend on the feel of the setting. Lots of gates in the world? Maybe it's a 6th level spell. Ridiculously powerful magic? Either it's a ritual, or it can only be cast by powerful supernaturals after much bargaining.