I didn't enjoy Shadow of the Erdtree quite as much as the base game, but it is still an incredible expansion that embiggens everything about the base game in meaningful ways.

The sheer size of this thing is out of control, with a density for most areas that is much higher than the lands between. This team knows how to make areas that surprise simply by their presence and how to pack an incredible amount of unique and interesting stuff into every corner of this world. I loved almost every minute of exploring this new area.
New weapon and magic types abound as well and many of them feel much different from the weapons on the base game. I picked up a pair of backhand blades early, maxed them out, and used them until the end of the game but things like martial arts weapons, light greatswords, heavy katanas, and perfume bottles make me want to explore even more of these options.

The bosses are less repetitive in Shadow of the Erdtree. There aren't a ton that you will face over and over like you do the fire lizards and cat statues in the base game. However, many of the minibosses you fight are basically a human with a special weapon or moveset which is fun, but not really surprising or impressive. I do think this is a better approach to limiting the scope here, though, and there is something cool about fighting a unique enemy then picking up their gear and adopting their fighting style.
The bosses that are spectacle are really impressive but definitely lean on the more generic From Software boss design of just forcing you to dodge a bunch of huge attacks. I usually prefer bosses with a gimmick or weakness for you to exploit and the expansion is largely devoid of those, unfortunately. It felt like a lot of the time I was just brute forcing the bosses or I was capped by how high my Scadutree Blessing was.

The blessing is a very cool solve for the scaling problem this expansion would otherwise have. Collecting shards around the world let you gain a stacking percentage attack and defense buff that juices your power level in the extreme over the course of the expansion (but only applies IN the expansion). So no matter your power level when you come in, you will probably be able to face most of the challenges here provided you explore thoroughly. I love that this rewarded me for all the exploration I wanted to do anyway and gave me a concrete reason to leave a boss I was having trouble with to come back later.

Narratively, this expansion was pretty hit or miss with me. I think it hard to slot something into the base game's endings and they sort of just don't really try. This area is split from the real world and the result of your time here is that you got some more information about a character who doesn't impact the search for the Elden Lord really at all.
I do like the way the narrative presents all these disparate people being controlled by Miquella, coming to their senses, and then pursuing their own goals or revenge but it is a bit too specific of a story that isn't told that well. I don't think this is really From's strongest skill and the storytelling method hurts them. Relying only on moving NPCs from location to location where they deliver cryptic dialog tangentially related to your actions just doesn't work that well. The major beats (breaking Miquella's spell, for instance) being tied to arbitrary area triggers also makes things unclear and ruins some of the payoff.
The individual characters are cool. I really liked Ansbach as this failed guard coming to terms with his failure and the player's part in it.
Igon the dragon slayer is actually the best From Software NPC to date. CURSE YOU BAYLE! I can't get enough of this depressed, broken, revenge obsessed, madman.

If you like the base game, play this. It is just a really solid expansion all around that brings a ton of meaningful weapon options, new bosses, and interesting areas to explore.

My review of the original.

The original Dark Souls II is an ok game that moves the series to a new engine, tries some novel things, and fails in a lot of ways. I enjoyed it enough at the time, but I don't think it holds up that well and is definitely the worst of the three Souls games.

Scholar of the First Sin, billed as "fixing" what was wrong with Dark Souls 2 only seems to double down on the problems while fixing none of the glaring issues.
Enemy placement is more tedious. Tough enemies are strewn about arbitrarily, making the already supremely annoying runbacks even more trying. In other locations, large mobs of regular enemies are haphazardly added, turning things from measured to chaotic in a way that the game and systems hardly support.
The DLC is built more directly into the game, but is hidden, making these arbitrary keys even more arbitrary and missable unless you just look them up.

Adaptability and the egregious enemy tracking remain. Power stance isn't any more obvious or exposed than it was in the base game.

Just play the original. Don't bother with Scholar of the First Sin.

Dark Souls II is mostly fine but falls pretty short of the rest of From's SoulsBourne catalog. It feels like you can feel the struggle with the new engine and lack of Miyazaki in every nook and cranny of this game.

DS2 is a pretty straight visual upgrade from DS1 that doesn't try to do much that is novel besides the new light sources. It all definitely looks like a Dark Souls game, but it does feel more like a remix than a second album. Some standout areas like Majula are really beautiful but nothing else really sticks with me in the same way the environments from the original do.
The dynamic lighting is pretty at times but feels more like an annoying gimmick than a real value add, for the most part. I believe targeting range is reduced in the dark, even though you can actually see your target which feels very bad.

Dark Souls II just plays differently from other souls games in a way that isn't very obvious. Some of it is the reviled adaptability stat, but the input and animations just feel more sluggish and unresponsive in general. You definitely get used to it and once you put some points into agility things become manageable, but things don't feel immediately good to play in this game, unfortunately. Enemy tracking is also very extreme, which exacerbates this even further.
DS2 has some cool systems in play that try to differentiate it from its brothers. Chief among them is the power stance for dual wielding. If you have enough (it is a hidden value, blech) of a stat, you can enter a special stance (with an unmarked button chord) to dual wield two weapons, giving you a special moveset and options. This is really cool and I liked playing around with dual wielding in a way that souls games up to this point never really supported. In practice, the spotty dodges and enemy tracking made me fall back to a shield, but it is cool that they are trying things out here.
There are some cool boss fights (especially in the DLC) but for the most part bosses are large and lumbering with a 3-hit attack string that you can easily circle around and kill without much trouble. I wish there were more like the horseman in the Undead Purgatory, with truly weird mechanics and interactions (though that one in particular is MASSIVELY undermined by the runback).

Some of the levels are fun individually to explore and Dark Souls 2 features a lot of environment changing interactions, which make things feel a bit more dynamic. Tedious bonfire and enemy placement undermine this almost entirely though, as you are often forced to slog through massive, enemy choked sections of levels again and again when you die. Many sections of the game are simply grueling (No-Man's Wharf, Huntsman's Copse, and Shrine of Amana are the worst offenders), forcing enough playthroughs to hit the respawn limit they added for this game. It is welcome when things stop spawning but feels pretty bad all the same.
On top of the encounter design, the world layout is linear but nonsensical. Most of the areas don't have any sort of coherent connection to each other and by the end you haven't really gotten any sense of the shape of the world as a whole -- one of the strongest aspects of Dark Souls. Seas of lava positioned on top of a field of windmills are just too obviously incongruous to be ignored.

Not quite a retread of Dark Souls, the narrative here gestures at some cool things, though the interest is backgrounded rather than foregrounded. I don't care even a little bit about the queen or the current problems of the kingdom. I love the giants and their ancient war, I love going into their memories to recover macguffins, and I love the relation this world sort of tangentially has to the world of Dark Souls. The uninspiring foreground is reason enough to go on this quest, but doesn't drive things effectively.

I definitely don't feel positively about this game but it does still have some measure of the From Software magic about it. On a first playthrough the tedium leans towards feelings of challenge and excitement and enemies and environments are threatening enough that the cracks in their behaviors and layouts are less relevant. If you have played every other soulsbourne game, this one might be worth a shot.