First week or so of the season were super fun when people were just trying out random shit. Now that everyone started melee cleaving, the game basically became super boring to play and honestly, this is the first time I've thought to myself "heh, I might not bother queueing for the rest of the season".
The mechanics/fluidity of the game feels better than MoP/WoD ( other than the remaining instant CC still in the game ), however all of the improvements they actually made with Legion is overshadowed by how disgusting melee cleaves are and how much damage+pressure they do. The game pacing is ( almost ) perfect, there is almost no scripted PvP like there was in WoD, ordinary DPS rotation actually matters outside of cooldowns, but all of that is moot in a meta where if you're not playing 2x melee DPS+healer, you're doing it wrong.
You can obviously do fine as a caster ( RMP, Hpala Shatter, etc ), but it's not fun in the slightest.
If you do a mistake, you should pay for it - that was always my opinion when it came to this game's PvP, and everyone should be able to punish you HARD for that mistake ( melee cleavers, melee/caster/healer players, spell cleavers ) - current meta is basically 2 melee training one target until it dies, and your target rarely can do shit about it. There are also a lot of dumb mechanics to compliment this. For example, why is current spell reflect a thing? WHY does it not consume the spell after reflecting something?
I still stand by my stance that Legion is the best expansion they've produced in ages. World content is fun, raiding is fun, mythic+ instance system is fun, artifacts are fun, professions are fun etc. PvP would be fun if melees weren't so ridiculously strong.