It has amazing classes, while not as good as they used to be and Legions is taking even more abilities, they are still more fun to play than other class based MMOs
Pretty much every race has a starting area. And there is a huge tree of zones you can level through, so each alt can have a very different leveling experience, and each zone looks very unique. Most MMOs still to this day don't have a starting area for each race...EQ does last I checked, EQ2 used to (pretty sure) but they removed that for some reason. Vanguard Saga of Heroes did, but that is gone.
Or you can solo dungeons to level (some classes its possible), or group harder dungeons to level, or pvp, or craft/harvest to level (one character ONLY crafted/harvested to max level (back in MoP) and made a lot of money doing that.
TONS of group content at later levels, but also a lot of solo content, so there is always something to do depending what you feel
You can play as Undead (almost no game lets you play as undead, granted they are Forsaken, pretty much same :P). Mostly strategy games have playable undead, like the upcoming warhammer total war.
You can play as Tauren (sorta similar to Minotaurs I suppose, but the lore of Tauren is epic and I love the native-american theme they have)
Troll race is epic, awesome lore
Lore in general in WoW is awesome (though its kinda iffy where they are going with things lately. I feel after WoTLK it was weird. Didn't like Cataclysm lore, MoP was okay (most don't like it cause of Pandas), WoD is meh just revisiting things), and SO much of it. But that is partly because Warcraft itself has been around a while.
Just a ton of contents to do. As a completitionist, to get to 100% achievements takes SO long, still not even close. Granted WoW has been out a while, but still offers tons to do.
Really unique cities, and they are pretty nicely sized. They are very lively (especially Stormwind), and really nice atmosphere in them. I think GW2 has better cities though overall
You can swim underwater. When a new MMO is released that doesn't allow underwater swimming, I go WTF? am I back in 2001 age of MMO movement mechanics? And log out and quit to never play again. I know kinda simple thing (but tons of people quit Saga of (Ryzom) due to lack of jumping), but swimming underwater should be part of every game. Even singleplayer games like Fallout 4 and Skyrim, even Oblivion that is much older, allow underwater swimming. No idea why a new MMO doesn't allow that. At least black desert online and GW2 is modern enough to allow it. Dunno, maybe most devs are smoking a pipe when designing the movement system lol.
My very first memory of WoW was making a troll in end of beta (got it from Fileplanet), going to Sen'jin, swimming underwater and I went "holy shit this is best MMO ever, I'm freaking swimming never seen that in an MMO before.". I was super excited just for that. That was the best first experience I ever had in an MMO. EQ2 allows underwater swimming and that came out about same time, but I got into EQ2 much later after WoW.
You can fly. A lot of MMOs don't allow that, but it allows just another type of advanced MMO movement system. But I find its probably because most MMOs are too small of a world, and WoW world is actually pretty large as far as MMOs go. If you run everywhere, it actually takes quite a lot of time to get through each zone.
(these next couple kinda relate to when I said each class is amazing)
Amazingly made Druid class. Even in WoD, the Druid is by far my favorite druid in an MMO. Vanguard Saga of heroes had an amazing Druid too, but unlike most MMO's and games, WoW Druid is a permanent shapeshifting class...a lot of Druids, the shapeshifting is very short/temporary in a game. And Druid in Legion is AMAZING. In fact, Blizzard has probably put way too much attention to the Druid lol.
Amazingly made Shaman class. I love the totems, and especially as a Tauren, it adds to the native american feel. Still testing it in Legions, but enhancement is awesome, elemental is meh as of now. However, elemental feels better than in WoD, just needs balance.
Warlock (only in WoD and before that) class is pretty cool summoning demons, a lot of MMOs and games in general don't let you summon demons. Legions dunno, not feeling it as much. Feels kinda clunky. Don't like dealing with limited shards. Demonology is probably my favorite spec in legions for warlocks, just cause I like summoning demons.
Going back to movement. It feels VERY smooth. A lot of MMOs have too clunky of movement, and this proves true in combat for WoW which feels great. I'd say only riding a mount is meh, cause your character looks like a frozen test dummy when riding mounts. And some mounts have a terrible rapid bouncing animation that really hurts my eyes.
A lot of MMOs just don't offer nearly a small portion of what WoW has. So I try new MMOs, then go back to WoW lol. And I really really want a new MMO, but WoW has so much to offer, so much variety, content and all the leveling paths is immense. It might have lost a lot of subscribers, but I still have yet to find an MMO that is more fun than WoW
Only two exceptions have proven that an MMO can make me enjoy it as much as I do WoW. Cities of Heroes and Vanguard Saga of Heroes (which had EPIC classes too)...sadly both those are dead.
My Skyrim, Fallout 4, Starbound and WoW + other game mods at MODDB: