The levelling experience in Legion was great!
- flexibility in levelling routes/zones
- most levels seemed well paced (I believe 100-105 was fine, then felt slow till 107 -then 107-110 was again a blast)
- no launch issues
- loads of profession/sideline distractions if you want that
- WQs to progress ilvl/Rep, if you need them
- pretty cool story in my opinion
- beautiful artwork
- fun mechanics to get you around, felt like you were 'exploring'
Personally, I still hold that MoP featured the most beautiful artwork and soundtrack (Heart of Pandaria imo is a masterpiece).
I do wish that the WoW experience could deliver more interactive story telling (via Scenarios or instanced events -like Broken Isles) but hopefully Broken Isles will be a step towards that. I think we've seen a pretty decent levelling experience so far, my only critique is that I'd be hesitant to level alts... but then that makes your main feel more important, and I have no problem with that -especially with Flying arriving in a future expansion.