Personally I've found this expansion quite good so far. The only real issue I see is what JG mentioned about having to be somewhat sure about the team you are rolling, or having to deal with a lot of regrinding. However if you already know the specs you want to play, you're in a decent spot. The amount of solo content is mainly bound to leveling and your order hall quest lines, so once you're done with those, it's pretty much done with.

As far as viability, it's looking fine. People are already clearing mythic dungeon content, so atleast 5-man content is perfectly reasonable to do, although do not expect it to be easy. With more focus on individual movement mechanics I'd be surprised to see anyone "solo" box normal raids for a good while. So far it seems you can maintain OK gear just from world questing, world bosses and LFR, so there's definitely a place for boxing casually as well. I'm mainly just chilling, doing world content and working on finishing order hall quest lines and professions and I'm slowly creeping towards 840 ilvl on my 8 toons. They're pretty repetitive, but as long as they are easy upgrades, I'm fine with it.

The PVP world quests are somewhat lackluster. There's no actual PVP to speak of, as for the most part you're just going around killing faction NPCs. There are a few free-for-all ones (which you can still do in a party) but in the normal ones there is no insentive for the other faction to be "defending".