The community: the fact that strangers voluntarily cooperate to get things done more efficiently without being forced by things like forced instance grouping.
Choice of difficulty by choosing whether to do green quests or red quests or something in between is a close second.
The biggest draws for me are the zones being in their original forms and having been able to be there at the start. I missed Vanilla launch and heard lots of stories of āthe early daysā when I started in 2005. Classic is a very real opportunity to go back and redo things āknowing then what I know nowā.
The community is great. Players are talking so much trash in trade and zone chat itās glorious. I am not even sure there is zone chat in retail.
This might sound weird, but I really enjoy figuring out ways to grind gold for my mount. Working the economy is fun. Gold and gear is limited which makes getting these things feel super special. I donāt even think about gold in retail, not sure when I ever even checked my bags to see how much gold I have, it does not matter at all.
I play a priest and I absolutely enjoy healing. I get to use different ranks, and I have to actually use my brain when pressing my buttons or else I got OOM. I have a actual mana bar again.
I am just really enjoying myself. Canāt wait to get home and continue farming gold for my mount.
Killing people.
Back in the day people used to farm there until the mobs went gray because the vendor garbage from those turtles and basilisks would sell for a good amount and Gadzetzan was nearby. After that, the coast of Tanaris was the good place to farm for people who dinged 40 but couldnāt afford their mount yet.
Playing an actual MMO again with IRL friends.
That and phat chain lightning crits on unsuspecting alliance players.
I donāt even know where to begin with the listā¦I meanā¦everything. Everything is better
I enjoy not feeling like Iām missing out just because Iām not level 60.
I said it before and Iāll keep saying it, but a lot of retailās current problems could be remedied if they gave players a reason to play outside of raiding. So many problems with the current game have everything to do with content just funneling you towards raiding. I want my professions to matter. I want to economy to mean something. I want PvP to be its own, cohesive experience rather than a subsidiary of PvE.
I want to enjoy the world, not parts of the world. I canāt do that when the game is constantly expecting me to be geared for the Next Big Update.
Yeah fishing those pools gave me a lot of cloth and leather that I was able to turn into a mount as soon as I hit 40.
Iām still afraid of Angry Turtle Beach though. Just swimming down the coast looking for pools and next thing I know some skull level turtle eats my face.
seeing familiar faces and having a realm community vs a swarm of randos
The game is focused on the leveling experience which isnt really possible in an expansion.
The things you canāt describe
I am enjoying various things but the most is QUESTING. You know, some quest are something forgetable, but some other are just pure gold.
Good quests talk about stories, dungeons and human characteristics of the NPC and the community. The fact that you donāt have the arrow indicating which way you should go, makes you read and understand the quest. Therefore, you are inmersed in the story, you are not a human controlling a fantasy character: you are the fantasy character, at least for a couple of hours of game play.
Some of the quests I enjoyed are: Succubus chain quest for Warlock, Test of lore (it is a long quest chain) and RFC quest chains with Thrall.
Iām also enjoying using my potions, my food and talking about lore in /1 and my brother while turning in quests.
In Warcraft Classic, you feel like a Warcraft III mercenary or just an ally of a faction, doing itās own way to be useful for the fantasy community.
I apologize for any spelling error
Regards
Seriously I canāt mash 
on this post hard enough.
Opening the talent tree every time I ding a new level and seeing that progressing, knowing each point is adding incrementally to my characterās ability.
Going to the class trainer every couple levels, watching my coin go buh-bye, but picking up abilities that help me go right back out and earn more coin.
Having access to ALL my basic class skills / spells, instead of being āprotā stripping me down to defensive stuff and āarmsā stripping me down to slow hard-hitting stuff.
Quests that give me an item to read that tells me where to go to get several items, sending me to both continents and even a dungeon (working on Brutal Armor for warriors, for example) because NPCs arenāt unaware a world exists outside their little bubble.
Trainers
Skill trees
Meaningful rewards
Useful Profession
Seeing people doing content all over and grouping
The space of the world
It isnāt retail.
The slow pace allows for more immersion, since youāre not rushing past the world to get to the next quest point.
Heck, finding the next quest point often does more to immerse you in the world than eighteen books on the subject.
Also, the story continues directly from Frozen Throne, as opposed to Retail, which created a massive continuity gap for reasons that, while I can understand, absolutely do not agree with.
One thing I like is that currency matters in Classic. I was actually excited to find a barrel of milk so I could save a silver by not needing to buy from a vendor. I also drank my milk well into my teens because melon juice costs 5 silver per 5 stack. 
Iād be fine playing the game without any raiding at all.