The vast majority of racials are either useless in M+ or so minor that your choice of race doesn’t matter. However each faction has a handful of racials that are impactful in M+, a few of which are legitimately game-changing.
Let’s start with the crowd favorite:
奥术洪流. Blood Elves get an AoE silence on a 90s cooldown that can also be used as a single target interrupt. Both uses are equally good. Being able to shut down a pack of casters (e.g., the Thundercallers in Halls of Valor or the Withered Fiends in Arcway) is an enormous advantage in high keys where one round of casts can kill people. And having an extra interrupt for fights like Medivh or Helya can make things significantly easier. As racials go, this one is the gold standard.
影遁 is a Night Elf racial that allows the user to stealth whether in combat or not. This can be useful in some dungeons as a way to skip trash (Night Elf pulls mobs to the side, group runs past, Night Elf Shadowmelds to reset mobs). It also allows you to negate some boss mechanics: Medivh’s
炼狱箭 and
霜寒 can be cancelled mid cast by Shadowmeld, and Wrath of Azshara’s
压抑深渊 can be removed by a player by using Shadowmeld. It’s a bit more niche than Arcane Torrent but certainly valuable.
石像形态 is another racial (Dwarves) that has limited but powerful uses. It can remove some boss mechanics, e.g., Moroes’ Garrote, and it can be used to reset stacks of Grievous. It’s not useful in every dungeon but it can definitely be a lifesaver in the right circumstances.
There are a few other racials that have general usefulness.
疾步夜行 can be used to kite mobs;
战争践踏 and
蛮牛冲撞 can be used as a last ditch stun;
奥术脉冲 can slow a pack of mobs. These abilities are less useful versions of other abilities in the game, though, so their value depends on you having a group comp that lacks certain things.