There are six spells of 7th level for illusionists in AD&D, the same number as in OD&D. The only difference is that maze has been replaced by first level magic-user spells.
Alter Reality: This spell is similar to limited wish, meaning that it can accomplish pretty much anything the caster desires, albeit partially or with a limited duration. The major difference is that the illusionist must first visualise the effect they want with a phantasmal force. (I assume this requires a separate casting of that spell, and isn't included as part of alter reality.)
The OD&D spell is the same, although it only requires the casting of an illusion, not phantasmal force specifically.
Astral Spell: Like the 7th level cleric spell, this allows the caster to project into the Astral Plane, and from there enter the Outer Planes. Check out this earlier post for my thoughts on the cleric version of the spell, and how it interacts with Gygax's previous writings on the planes.
The OD&D spell seems to have been intended to allow the caster to explore the material plane in an astral form, rather than granting travel to other planes. It doesn't mention the planes at all, as the spell was created before Gary had published his ideas about D&D cosmology.
Prismatic Spray: The caster fires seven rays, each of a different color and effect. The ray that strikes the target is determined randomly, and it's possible that multiple rays may strike the target. The various effects refer back to prismatic sphere, which I'll recap here: red - inflicts 10 damage; orange - inflicts 20 damage; yellow - inflicts 40 damage; green - save vs. poison or die; blue - save vs. petrification or turned to stone; indigo - save vs wand or driven insane; violet - save vs. magic or sent to another plane.
Prismatic spray was mentioned in OD&D, as a new spell in an article from The Dragon #1. But although it was in the list of new spells, it didn't actually get a proper description. This is the first time that the spell has been given concrete rules.
Prismatic Wall: This spell is also similar to prismatic sphere, but it creates a wall that is 4' wide per caster level, and 2' high per level. Anyone passing through is subject to all of the effects listed above under prismatic spray. Each colour can be dispelled with a specific spell.
In OD&D, the red, orange and yellow colours did slightly more damage. The indigo colour turned creatures into crystal rather than driving them insane. And the violet colour drive characters insane rather than sending them to another plane.
Vision: The caster contacts some sort of supernatural enemy, and asks a question which may be answered with a vision. The result of this contact is determined randomly. A high roll results in a useful vision, a medium roll results in a vision that may or may not be relevant, and a low roll results in the entity being annoyed and hitting the caster with a geas or quest. The material component is the sacrifice of something important to the caster or the entity, and something very precious will grant a bonus to the roll.
The OD&D spell doesn't specifically say that the reply comes in a vision. It uses the NPC Reaction Tables to determine the result, but it is otherwise the same. There's no mention of material components, though.
First-Level Magic-User Spells: Instead of gaining a 7th-level spell, the caster gains a number of 1st-level magic-user spells. The list of spells to choose from isn't complete: dancing lights, detect magic, find familiar, identify, jump, light, push, spider climb, ventriloquism and write aren't included. The illusionist gains four spells at 14th level, and an additional one per level above that - presumably this isn't set in stone when the spell is cast, and the caster keeps gaining m-u spells as they level up. They don't get the spells automatically, though - they must seek them out like a magic-user. To my mind this seems weak for a 7th-level spell, but I suppose it does give the illusionist a little more utility. And magic missile is a pretty good spell even at high levels.
The OD&D version of the spell was 4th level, and allowed the illusionist the use of every 1st-level magic-user spell. No doubt Gary decided that this was too powerful, and pulled it back. There was also a 5th-level spell that granted the use of all 2nd-level magic-user spells, but that was completely gotten rid of.
Some illusionist end-notes: So that's the end of the illusionist spell list, and the end of the PHB spells entirely. Going back over my notes, I was reminded that the Illusionist spell list was rolled out in a piecemeal fashion. The class was introduced by Peter Aronson in The Strategic Review #4, which gave spells up to 5th level. For the most part they all made the transition, aside from the aforementioned 2nd-level magic-user spells. Another article by Aronson in The Dragon #1 brought in spell levels 6 and 7, as well as introducing some more lower level spells. Again, these made the cut for AD&D mostly unscathed.
There was a third article about illusionists by Rafael Ovalle in The Dragon #12, which brought in a lot of extra details about illusionists and introduced a load of new spells. None of these made it into the PHB, possibly because they were published too late. Whatever the reason, it seems like they faded into obscurity. I'll still have them in my Ultimate Sandbox campaign, but as spells that can be discovered in old tomes and scrolls rather than ones on the default spell list.