This new version is much better written, but still not clear enough. What does it mean to have AC 10? Is it the intent that spells that target creatures, like Ray of Frost, could damage it? Because there are only a few that target objects with a melee or ranged spell attack and deal the required damage types.

• Cold damage only has the new and Sorcerer-specific Sorcerous Burst and Chromatic Orb, which isn't clear on what a target is, so it could be a Prismatic Layer.
• Force damage has Blade of Disaster, Eldritch Blast and Mordenkainen's Sword.
• Fire damage has Chromatic Orb, Fire Bolt, Flame Blade, Produce Flame, Scorching Ray and Sorcerous Burst.

Being so incredibly specific and hard to counter means a high-level player has almost no reason not to use this spell in every important combat. And every one of these combat situations are reduced to a) high-intelligence enemies not going near it or b) at least one low-intelligence enemy trying to go through it and dying instantly. In both cases, players with ranged attacks will go out, attack and go back in every turn. Combat turns into a slog.

I found that the only way to kinda deal with it is with Cloudkill, which is not great because at higher levels poison damage is completely negated by half of most parties, or Lair Actions and Legendary Actions that aren't spells and don't rely on sight. Of course spellcasters could try to Counterspell it, but if you play fair, this is reserved to really high-intelligence arcane bosses that know what a Prismatic Wall is, and if they fail to counter it, we're back to square one.

I understand that a 9th-level spell must be powerful, but this is just boring. I've read every Reddit post on the subject, the Spell Spotlight article by James Haeck here on D&D Beyond, and even Pathfinder players with similar complaints all over the Internet. If anyone has any advice on how to make this not ruin every combat, I'm all ears.

A wall is classified as an object, and this spell creates a wall.

Anything that uses an attack roll with a d20 to hit something can target a creature or an object. (Melee attack, ranged attack, spell attacks)

If an attack spell does not specifically state that you must target 'a creature' within range, then you can choose to attack an object. The inclusion of 'a creature' is usually going to be what indicates limitations on targeting.

It is an amazing spell to protect something specific as it stops ranged attacks as long as the first two layers are still up and it stops spells as long as the last two are up. Keep in mind, you cant cast or attack from behind the wall with those layers up either. You, a designated creature, can pass through the wall unharmed, but not your attacks. The enemy would learn quickly what the negative effects of the wall are, then would essentially hold their actions to play whack-a-mole when your party peaks their heads out to attack. Either that or just wait it out until the spell ends in ten minutes. It does still make for an incredible spell during a climax like "we have to hold off all the demons pouring out of this portal for the next 5 minutes while the Rogue and Cleric undo the summoning circle!!"

Its amazing for specific situations and cutting off hordes from approaching you. However, with level 9 spells, every time you use this spell means you don't get to use a Power Word or a Wish that day.  It can be fun to have a party learn what one is and come up with a plan to disassemble one. My party was pulling off a high level heist, and we knew that we would have a 5 minute window to break through a Prismatic Wall if we wanted to get past a certain section. It was super fun when used against us like that.

Why is this spell classified as Abjuration? Seems to me it should be evocation. 

It is a barrier....you are guarding, not evoking. 

Yeah, but Wall of Fire, Force, Ice, Light, Sand, Stone, Water are all evocation spells. 

Because you are putting up a wall to tell enemies "no, you can't come here"

it is a hold over from previous editions. but its also a 9th level spell.

Maybe this will help expand horizons and give some ideas. 

I let the enemy use this to protect herself while the party battled minions and tried to stop her. She was opening a gate to Avernus and summoning stronger and stronger enemies each round, so the party had to deal with the enemies AND try to get to her. They were able to roll arcana checks to determine what her spell was and how to counter each layer as they encountered it, so it was a multi-tiered battle. For some of the more obscure damage types, I placed usable items on the map (catapults, arcane bolt throwers, lava etc.) that they were able to get creative with. 

From what I've seen as a DM, all spells CAN be used by the party, but not all spells are necessarily FOR the party.

Hope this helps.

If you were to apply the Sorcerer's Metamagic Option;Transmuted Spell, would one application change all energy types to a single one? or would you only be able to change one layer per sorcery point?

Basically could you apply it once to make all layers dealing only Thunder damage (those layers with an energy) and then apply the Tempest domain cleric's ability to maximize damage dealing 72 Thunder damager per layer for a total of anywhere from 60-360 Thunder damage (depending on save)?