Legion contains some of the best content the Blizzard team has delivered in years, but WoW's aging engine and toxic community somewhat dampen the experience. At this late stage in the games development history, there is little to recommend for a new player. This review is primarily aimed at past player's who are trying yo decide whether to re-sub for Legion.
It depends is the best answer I can give. Questing beyond level cap essentially amounts to World Quests, which are a slight tweak to the dailies of past expansions. The instanced content is generally pretty solid at all levels, and there are effective tools for finding groups if you aren't returning to a guild.
The engine is showing its age, and doesn't run well on some modern computers. I've never had issues with it in the past, but on my current build I sometimes get unplayable framerates, even though I can run more modern titles without issue. Your mileage may vary, but the obsolete technology of WoW is not well optimized for today's PCs.
If you enjoyed WoW in the past, Legion is probably worth checking out. The game has more or less exhausted it's appeal for me, and I won't maintain a long term subscription, but I don't regret the purchase or the play-through.