I made a Lightforged Disc priest and it was incredibly rewarding, at least before my old guildies forced me back to lock. Disc has amazing cooldowns, can do damage, good heals, and can survive the melee train for a time. Going from Disc priest to warlock felt terrible for that reason. Once you receive the legacy armor, Lightforged Disc feels like a battle priest.
Apart from some issues, I enjoy BFA thus far. Mythic Siege of Boralus was incredibly fun and reminded me of a vanilla dungeon runs, where the group had to coordinate together or fail. I am actually glad Blizzard tied it to a Mythic, because it was a rewarding way to finish the storyline.
One of those issues for me is that class balance and philosophy seems to be in a strange place. Specifically, my impression was the Blizzard intended for each class/spec to have upsides and downsides to create a sense of a trade off. Yet, some classes do not appear to have a downside, particularly when you factor in mobility. For example, Affliction is incredibly strong in certain PVE and PVP situations, but can be complete ass outside of that niche (e.g, burst AoE). Therefore, Affliction seems to meet the design intent. In contrast, when I switch to Demon Hunter, the class seems to have great mobility, utility, damage, and survivability. I am not seeing the downside. Similarly, I am not sure what the downside is to Frost Mage. Perhaps is a "grass is greener on the other side" moment, but high mobility classes seem to be in a great spot.