If you have a decent memory about the various versions of World of Warcraft, you may notice that WoW Classic is not quite the same as the Mists of Pandaria you remember on expansion launch. Hashtag some changes after all. Actually, based on the list of patch notes, it would be more accurate to say hashtag a very large number of changes, which you can find out about in the patch notes as cited. There are many, many changes.
Among those changes are the absence of the raid finder (does this remind you of anything), changes to reputation gain to speed up the early stages of progression for players reaching the level cap, and the addition of new Celestial Dungeons (which functionally occupy a similar spot to Mythic+ dungeons in the retail game). Check out the full rundown for all of the changes that have come to the game in its newest incarnation.