There’s a pretty bad case with a lot of classes having spells with hard to read or straight up ancient spell effects, sound and visually. I will do my best to list them all here, but take into account that this is not exhaustive in the slightest.
Personally, with the leaps and bounds in vfx advancement since 7.3, some classes may need another pass at full spell effect updates, but this is largely to highlight spells that were untouched from that update.
Mage
Cold Snap, Alter Time, Feather Fall, Ice Barrier, Ring of Frost, Slow, Spellsteal, Ice Block.
Most of Mage’s untouched spells are in the utility category. Though their fire and arcane effects definitely could use a touchup compared to what is in Dragonflight, these are the worst offenders for mage.
Druid
Renewal, Heart of the Wild, Regrowth, Renewal, Swiftmend, Innervate.
A lot of Druid’s offenders are the basic healing spells using old leaf effects. Compared to spells like Wild Growth, most of them look a little dated. (Feel free to disagree on this one, I’m not a druid main by any means.)
Shaman
Oh god. So much of it, but this is about ones that never got an update.
Chain Lightning, Windfury Weapon, Flametongue Weapon, Doom Winds, Ascendance, Lightning Lasso, Lightning Shield, Water Shield, Earth Shield, Nature’s Swiftness, Gust of Wind, Thunderstorm.
Shaman is plagued by a lot of missing updates on spell effects. Doom Winds and Windfury weapon in particular are flat out so understated effects wise that you can hardly tell when they’ve been activated. While again most of their outdated effects are utility, some are in the main damage category- Chain Lightning is a big offender here, especially since it had a completed effect ready in 7.3.
Priest
Halo, Power Word: Shield, Purge the Wicked / Holy Fire, Prayer of Mending, Apotheosis, Symbol of Hope, Holy Word: Serenity, Holy Word: Chastise, Prayer of Healing, Dark Ascension, Mind Spike, Mind Sear.
Priest has the issue that much of its outdated FX are from mainline spells and cooldowns- in particular, Mind Spike being the upcoming filler replacement to Mind Flay, Hoy Fire and Power Word: Shield being signatures of their specs, and Mind Sear being a common aoe pick all having vanilla appearances are quite frankly, disappointing.
Warlock
Drain Soul, Soul Fire, Dark Pact, Mortal Coil, Shadowflame, Unending Resolve, Health Funnel, Fear, Banish, Burning Rush, Shadowfury, Vile Taint, Haunt, Dimensional Rift, Cataclysm, Channel Demonfire
Warlock’s case is pretty egregious. Almost every one of these spells listed aren’t just situational, occasional needed utility, but mainline damage spells. Often times these have an in-hand cast effect that is up to date, but projectiles that remain as they were in 2006.
So what’s the solution?
Well quite frankly, I just want Blizzard to just take a glance at some of these spells and make them have more modern effects to bring them in line with the rest of the caster’s kit. If I were to pick only two classes in desperate need of that look over, I would say Shaman and Warlock need this the most, though for different reasons. The issue with Shamans- especially the Enhancement ones listed- is lack of readability. The issue with Warlock, though, is simple neglect. I hope this can bring their attention to updating these spells to bring them in line with the modern look of the caster’s kits.