ROFL
The biggest reason Legion is not praised universally and is usually viewed as "good, certainly better than WoD, but ..." is class design / ability pruning. Talk about a completely unnecessary turmoil that took tons of development resources and made many things worse instead of better.
And the second biggest reason is PVP not just being in ruins as is usual in the first patch of every addon, but being such crap that the ladder is now about 60% of what it was during WoD. Yes, really. I figure you don't really PVP and are talking about things like PVP talents just because you heard something about them and thought that they should be good. Surprise - PVP talents are perhaps not a bad thing, but they are a small nit in a sea of changes, and other big changes which affect PVP were terrible.