The DLC story is longer than regular season story add-ons but not that much longer so from a pure story point of view not sure it's worth it (I wouldn't pay that much just for the story). I did enjoy it though. It's also a good way to get a character up to max-ish level even on the first difficulty.. no more having to jump up tiers as soon as possible. Makes getting to the end game almost too fast.
The Spiritborn class is pretty good though, I mean it was pretty ridiculously broken for season 6 but there are bug fixes coming that will shave that down quite a bit, but it still is one of my favourite classes to play and will probably be the strongest class for a while. I just don't really like the aesthetic of the class unfortunately.
Runes are also behind the DLC but they aren't that important at this point; I don't think there's any build that really depends on them. Though they are getting some buffs.
Though there's one HUGE thing with runes that I'm not sure if they're fixing.. if you want to craft a specific mythic unique (the rarest and most powerful items in the game) to do a specific build the recipe requires runes. So if you want a specific mythic unique without the DLC you have to farm for them. Which isn't that different than farming for runes I guess. And you don't NEED a mythic unique to be powerful, it's only if you want to push the highest torment levels.
The DLC includes a new area which I do like; the mob density there just feels higher than all the other areas. Not as good as a Helltide of course and those are always up but still.
The biggest thing though I think is the additional endgame activities VoH has. Kurast Undercity is fun and allows for more targeted rewards.. you can focus on getting more resources or gear or runes or even skew the random gear rolls towards the affixes on the gear you want.
Between the Spiritborn class and Kurast Undercity that made the expansion worth it to me. Plus the ride-able cat
Plus there's The Dark Citadel endgame activity which is more like a raid but requires multiple people to complete.. I haven't tried one so I can't comment on how fun or rewarding they are. I prefer to play solo.
That said there are still good endgame options without the DLC.. fighting bosses (something that also is best in groups at least from a resource efficiency point of view, you need materials to summon bosses and a group of 4 can summon 4 times as many bosses), Helltides, The Pit, Infernal Hoards, and Nightmare Dungeons. All of which have their own benefits and appeal.
