I use to read your blog for many years and I have been away from WoW since 2015... How is the game nowadays and what major changes have been made ? I plan on returning next week.Welcome back!
Since you say 2015, I'm guessing you missed Legion. The most noticeable changes Legion introduced are World Quests/Emissaries and Mythic Keystone dungeons.
World Quests/Emissaries replaced daily quests at max level. Instead of getting a bunch of dailies, when you open your map, there are a variety of quests scattered around the zones. Each day, there's an "Emissary" quest to do 4 World Quests from a specific area or faction.
Mythic Keystone dungeons (also called Mythic+) are extra-difficulty 5-man dungeons. They're timed runs which reward higher item level the more difficult the Keystone used to start them is. They're basically an alternate to raiding, and higher Keystones award comparable gear to Heroic and Mythic raiding.
Battle for Azeroth introduced Island Expeditions and Warfronts. They're lower difficulty than dungeons, and more optional activities. Their reception has been mixed, but they're worth trying out.
Otherwise the game is pretty much the same as ever. BfA has separate stories for each faction, so it's worth having both an Alliance and a Horde character.
Any other changes in the last couple of years worth talking about?
Edit: I completely forgot, but Legion added Demon Hunters, which are a pretty neat class.