I could tell you the zone design in Wrath is better, the music, the atmosphere, the quest design etc etc. I could tell you that. And it would be true imo. At least by comparison to BFA and Shadowlands.
But put simply, the gameplay loop is more satisfying.
In retail, which, I will go back to for a bit during Dragonflight; when you get a piece of gear, it’s never satisfying.
If you do a M+ 10 and get a decent belt or chest, there’s this niggling voice in the back of my head going, what’s the point, if you do this at +11, I can get the exact same item, just 3 ilvl higher… when I get a piece of gear, I want it to be impactful. Either because it’s bis, or maybe it’s situational. Like, example, the Shattrath Leggings or whatever you get from a quest in Netherstorm. I wore those for like 5 months on my Ret Pala. That’s satisfying, and it leaves you time to do other things in game, gear an alt or whatever.
Retail has you running around, farming rares all day for 1% drop chance mount, and to farm rep. If I’m farming rep, I want the dailies to give me a decent amount, and then boom, I’m done. I go play an alt, or I play a different game, or y’know, go outside. I don’t want to feel like I have to farm rares for 2 more hours. And in TBC, in most cases you’d be done in about a month, slightly longer. In BFA, man, the Uldum and Panda reps were a massive slog, with little to no reward at the end.
Retail is fine, but it doesn’t respect your time in the way Classic does. Even from a collection perspective, if you get a rare mount in Classic, it’s like, one of a handful of rare drop mounts. In Retail who cares if you get that 1% drop reskin of an old mount, there’s probably 20 other colour variations.
I’ve made it sound a bit like I hate retail. I don’t, I play both. Retail provides a level of challenge that Classic can’t. Raids are harder and have more mechanics, M+ keeps you on your toes.
But I prefer Classic because it’s simple I guess. It plays to WoWs strengths. It allows me to play the game I want to play it. In retail I feel like, you’re forced to engage with content in an unnatural way, there’re just so many gimmicks nowadays.