I'd agree that many boss fights in early WoW are very 'simple' by present day standards, but back then internet connections weren't as reliable as they are now so many design choices are pretty much a product of their time. More than anything, it's the world building and sense of scale that I miss the most. I'm the type of player who likes to go and explore in the games that I play. If there's a big, imposing mansion in the distance then I expect to be able to enter it and see what's inside. I liked how ARR had a bunch of buildings in settlements such as Aleport that could be entered - it helps make the zones feel more alive. Newer settlements are just a bunch of NPC's standing around buildings that, more often than not, are entirely closed.