Quite entertaining.
There is a lot of exploration in the game. The Draenor zones in particular reward the player for doing so. In fact, the only way to be able to fly in Draenor is to do most of the quests and explore the zone. Most of the mobs are trivial but there are scattered enemies throughout that pose a good challenge. Most of the quest hubs have a similar pattern. Get there, do 2 quests in a particular small area. Come back, turn those in and do 3 more. Come back, turn those in and get a quest to kill the boss who is a bit more challenging. Kill him and move to the next area. Then in Draenor there are mobs marked on my map with a star. These are zone boss mobs who will always drop a BOP blue or purple. Some of these guys are quite difficult.
Leveling is quite quick even without any boosts or heirlooms. I have gone from 80 to 100 with one character playing some nights and weekends. Because there is so much new content I do not feel like it is boring. The scenery and story usually keep me entertained. The challenge of pulling and killing enemies is long gone but in some ways maybe that is a good thing. I do not long for the days of Burning Crusade where quest after quest was “kill 15-30 of these” and each one took a minute to kill.
Another thing present in Draenor is your garrison. You essentially get to build your own town and the NPCs there provide quests. Later on there is a lot of grinding involved but it is kind of cool to see your little own area of WoW grow and prosper. I have not done anything in Legion but I am told it is the best expansion thus far.
As a returning player I have posted some recent impressions here: World of Warcraft: Legion