I dunno I just can't imagine anyone still playing this game 20 years later.
I resubbed last month to check out how things are going in WoW.
Servers are packed.
Doesn't matter if you want to play Dragonflight, Classic Vanilla, or Hardcore, there's more people online than I've ever seen. I didn't check Lich King, though.
Blizzard lets everyone play together in the same world independent from the realm a character was made on. So even if your realm population is shown as low, there are players everywhere.
Hardcore Classic is amazing. If your character dies, you can't resurrect on the hardcore server. You can either live on as a ghost on the hardcore server or transfer the char to a regular classic server for free to resurrect there. This makes raiding pretty intense.
WoW streamers made a tournament on hardcore servers this week where they dueled to death with their level 60 characters. Lose the duel = your character is gone.
Normal classic servers are a laid-back and very social experience. It still feels much more like an mmorpg than every other mmo game that came after it and than every wow expansion. Most players I met didn't even play the game back in 2005. Some of them weren't even born in 2005. You will need a lot of gold in classic, though as everything works with Gold Dragon Kill Points (GDKP).
I checked out Dragonflight as well and so far I like it. Dragon riding is awesome. Gameplay has become pretty complex, though. Combat is much faster than classic and I need macros to keep up with the amount of abilities.
I recommend starting a fresh level 1 character instead of using the level 60 boost to learn the new mechanics. Leveling to 70 is super fast.
There's a catch-up mechanic in Dragonflight called dreamsurge that gives you epic gear pretty fast as soon as you hit maxlevel. Game world is packed. My framerate drops pretty hard when I visit the new city because there are so many players.
Playing WoW back in 2005 is my all-time favorite gaming experience. I usually resub for three months during phases of high real-life stress. For me, casually playing WoW is the best anti-depressant. Works every time.