Time rifts. Literally everything about them appeals specifically to me - the obscure lore references, all the cosmetic rewards, goofy AU stuff like the Cenrrrn Cirrgl murlocs, even the skybox! It's by far my favorite community event of DF.
The Shadowlands zones. I don't think I'll ever get over how aesthetically my jam these zones were. Ardenweald is my favorite, but Bastion's got a special place in my heart and Revendreth is just downright S-tier in both vibes & appearance.
The different quest backdrop designs. It's a small thing, but I like seeing them pop up because they're so artsy and add a lot of flair to quests. The Night Fae design is probably my favorite of the bunch so far.
Sholazar Basin. All of the Wrath zones are honestly super nostalgic for me, but Sholazar was my comfort zone. I loved its vibes so much, I'd AFK there for hours or just fly around lazily while listening to the music and talking to friends.
The Serene Dreams spa quests in Thaldraszus. The whole thing had me in fits, I remember thinking it couldn't possibly get better when Baby jumped out and murdered a bunch of Primalists. It was great, absolutely 10/10 would save Baby again.
The Shaping of the World music track. I listened to it so much when I was younger, it has to be up there with Nightsong as one of my most favorite pieces in the game's whole soundtrack (even though it technically never made it into WoW).
Raid entrances. They're some of the best designed places and honestly one of the most iconic parts of the game for me. I have way too many favorites to choose just one (let alone four!), but I think Vault is definitely among the best.
Ner'zhul's MU story. I've always liked how tragic it was that he possessed a love so deep for his late wife he'd do whatever her "spirit" told him, only to find out he was being played by Kil'jaeden all along. Ner'zhul's regret and horror at his actions - not just because he'd committed an atrocious act, but because he had actually wronged his wife - was so compelling to me. And the fact that he thinks about Rulkan even at the end, that his first line in SoD is about her, totally breaks my heart.
Quest skips and being able to choose what order I'd like to do zones in. I always try to level through quests if I can, but it's really nice having the option to skip some required introductions/zones if I don't feel like doing them.
High elf customization options. Back when I used to roleplay, I mained a human priest who had a brief stint as a high elf. I got by on the Sin'dorei orb, some prisms, and a whoooole lot of imagination. I'd given her up by the time we got high elf customization options for our void elves, but seeing them added to the game made me so happy after all those years. I immediately race changed her and, I have to say, it just feels right finally being able to play her as the character I always envisioned her as.
Lore easter eggs. I am -such- a big fan of WoW's story and I get so giddy whenever I come across references to more obscure bits of lore in the game, like Broxigar's monument on Argus or the allusion to Valstann Staghelm (!!) in DF.
The new Darkmoon Harlequin transmog. I'm genuinely so in love with this mog, the jingle physics, and how high quality it looks. I wanna stare at it all day, I think I might actually have to level the character I mogged it on now.
The expedition & dragon racing world quests in Dragonflight. I thought these were the coolest thing ever when I did them for the first time, I don't know that I've ever logged on so excited to do WQs as I have this expansion.
The Path of Cenarius. It's a small thing, but back when I roleplayed I LOVED stuff like this because it did a lot for my character/class fantasy. Having my druid leave plants behind her as she walked just felt right, it made me so happy.
Backpack mogs. It took us SO long to get them but now that we finally have a few, my mog-obsessed heart is thriving. I genuinely think they're one of the best things we've gotten (next to glasses, of course).
The change that allows the player to use a quest item on an NPC by just clicking the NPC. It's a small thing, but it's soooo much more convenient than having to find the item in my inventory (or way over on the side of my screen) to use it.