I have played 800 hours in TW:WH 1 and am closing in on 1700 hours in TW:WH 2, so I may be biased here when it comes to the Total War: Warhammer series - but this is a great time to get the into the series with the winter sale. The most recent DLC came with a free quality-of-life patch that, among other things, massively reduced the end turn times and generally optimized a huge amount of things in the game. This makes even the longest campaigns much faster and more enjoyable.
If you're interested in getting this but don't want to navigate the ocean of available DLC, here's how I'd break it down as far as what to buy:
MUST BUYS:
TW:WH 2 is $20, and gets you the High Elves, Dark Elves, Lizardmen, and Skaven - along two campaigns: Vortex, which is the more structured, goal-oriented one, and Mortal Empires, which is the massive sandbox campaign that spans almost all of TW:WH 1 and TW:WH 2.
TW:WH 1 is only $15 on Steam right now, and that gets you the Empire, Dwarfs, Vampire Counts, Greenskins, and Bretonnia for use in Mortal Empires. All of these races (except Greenskins) have been majorly reworked to be up-to-par with the game 2 races, and Greenskins will get a free update in the spring.
STRONGLY RECOMMENDED DLC:
Curse of the Vampire Coast are $9.49, and are probably the best DLC race pack - they're a fun race that have a bunch of great campaign and battle mechanics that allow you to play the game in very unique ways.
Rise of the Tomb Kings gives you access to the Tomb Kings (duh) for $9.49. They're another great faction that are well-worth playing - their unique approach to unit recruitment/upkeep make building your empires really enjoyable.
The Prophet & the Warlock is a Skaven/Lizardmen lord pack for $6, but it adds a ton of great stuff to Skaven - especially their weapons teams. Skaven in the base TW:WH 2 are a bit rough around the edges - this DLC smooths those out and adds strong new units/mechanics that make them much more enjoyable.
GOOD BUT NOT ESSENTIAL DLC:
The Queen & the Crone is a $4 lord pack for High Elves and Dark Elves, and fleshes out their rosters a bit more. If you're a huge High Elves fan, get this for the Sisters of Averlorn alone.
The Hunter & the Beast is a $9 lord pack for Lizardmen and adds a new Empire faction in both Vortex and Mortal Empires. It's not on sale yet, so you can probably wait on this one.
The Shadow & the Blade is another $9 lord pack for Dark Elves and Skaven, and is the newest DLC. Unless you're dying to play as Deathmaster Snikch , you can probably wait on this one too.
Norsca are a race pack for the first game, and are on sale for $5. They're the best of the game 1 DLC races, and have a fun Mortal Empires campaign where you can ride around the world like a Chaos Viking, pillaging and plundering.
The King & the Warlord (Dwarfs/Greenskins) and The Grim & the Grave (Empire/Vampire Counts) - both lord packs for game 1, both $4. Both pretty good and cheap additions to the races from the first game.
I HAVE EXTRA MONEY TO BURN AND REALLY LIKE THIS GAME DLC:
Blood for the Blood God - $3 gets you some blood textures that are overdone and kind of silly, but also enables the fun dismemberment kill animations. I wind up using a mod to tone the amount of blood splatter down, while still allowing my dudes to chop peoples heads off, rip them in two, and generally spice up the visuals a tiny bit.
Chaos Warriors - $4 gets you a playable Warriors of Chaos faction. Sadly, while they have one of the best rosters in the game with some of the deadliest lords, they also have one of the most boring, shitty campaign mechanics in their horde gameplay. Unless you are ready to mod the fuck out of them, you can probably pass.
Realm of the Wood Elves - $9.49 for Wood Elves. They're another faction hampered by bad campaign mechanics - Wood Elves can only permanently inhabit magical forest settlements (there's only around 7-8 on the whole Mortal Empires map, out of 200+ total settlements), and create weak little outposts everywhere else. They rely on "amber" from these outposts to do most of their upgrades/research/etc., and you'll constantly be losing them to everyone, everywhere. Unless you really have a soft spot for archer-based gameplay (or want to mod them to be less awful), you can pass.
Call of the Beastmen - $9.49 for the saddest race in Warhammer Fantasy. Combines the shitty horde mechanics of the Warriors of Chaos with the weakest, most pathetic battle roster in the game. Plus, as an evil, chaos-based race, almost everyone hates you and wants to kill you on sight. Enjoy spending dozens of turns hiding in forests, hoping that you can muster up enough gold and population growth to someday afford some Minotaurs, which are your only good unit. Another race that's only for obsessive nerds like myself.
CONCLUSION:
For $35 bucks, you get a ton of gameplay out of this series - even if you only buy the two core games, you'll almost certainly get your money's worth if you like the core Total War style of game. If I were jumping in fresh right now, I'd spend the $60 to get the two core games and the top-tier DLC, and then keep an eye on the other DLC if any one race really strikes your fancy as you start to play.