Remnant vs. Dark Souls

Remnant: From the Ashes is commonly described as ‘Dark Souls with Guns’ which isn’t entirely unfair. It shares the bonfire mechanic (now Crystals) where if you rest all enemies in the area respawns, with the trade-off being that your resources are also regenerated. Resources which include an Estus Flask like object (the Dragon Heart).
The Dragon Heart, like Dark Souls, starts with just three uses and can be upgraded for more uses between rests through rare items (Simulacrum, in this case).
You’ll spend your time opening short-cuts between areas. You’ll manage stamina. You’ll fight bosses. You’ll take items from said bosses to create new weapons. You’ll take other items of varying qualities to upgrade those items. And it’s balls-to-the-wall hard.
Whichever you choose to play — be prepared to die.

But there are differences. Some of them mechanical. Some philosophical. Some a mix! Areas have a certain degree of procedural generation in Remnant: From the Ashes. You won’t necessarily see all possible quests, events or bosses in a single playthrough of Remnant. Your world is created as you go.
It’s static within the context of that playthrough — you can revisit previous areas in future sessions and they’ll be the same. The difficulty of areas in Remnant, unlike Dark Souls, can vary. Remnant generates the difficulty of an area the first time you visit it, based on how powerful you are at the time.
But Remnant also allows you to ‘reroll’ your campaign world which will reshuffle everything. And since you’ll be visiting areas again for the ‘first time’, the difficulty (and loot drops) will scale with you right from the outset.

On top of that, you can — similar to other ARPGs — set a base difficulty for your campaign world, selecting from Normal, Hard or Nightmare. This is a large part of the replayability of Remnant.
Post-launch, Remnant also had an ‘Adventure’ mode added where you can generate individual planets rather than repeating the entire campaign. This is incredibly appreciated as you can hold both a full campaign and an adventure mode as ‘current’ for your character, switching between the two at will without needing to reroll your campaign to see the content you didn’t initially have spawn in.
But where the power of this game was seen, for me, was that Remnant acted as a gateway for interest in Dark Souls. Within my gaming friend group, I am an anomaly in having loved the Dark Souls games. A couple previously refused to even try them.
Yet something with Remnant: From the Ashes resonated well enough to get them interested. And since finishing the game there has been discussion of trying out Dark Souls in co-op too.
Remnant vs. Dark Souls for Multiplayer

When I consider Dark Souls — and even the broader set of Dark Souls-likes that include multiplayer, e.g., Nioh — I realise they think about multiplayer in quite a different light to Remnant.
Remnant while sharing many aspects with Dark Souls, welcomes multiplayer. It opens its arms to the idea of co-operative play. It shares more with the ARPG side of its lineage here than it does Dark Souls. You can freely bring in other players (albeit only 2 others) for an entire session. And freely.
There are no hurdles to jump through. No special status for your characters to be in, in order to host a game.
You bring friends in and they can stay until you or they decide otherwise. If you’re hosting — your friends can still gain items and gear. Drops (save ammo, which must be discussed or otherwise managed) are shared, even. No matter who picks it up, everyone gets it.
In contrast, by reason of design philosophy rather than technological limitation Dark Souls limits co-operative play heavily.
Dark Souls wants to emphasise the singleplayer elements. The struggle. Co-op is possible but it comes at a cost.
You need to restore humanity (DS I & II) or be enkindled (DS III) in order to even see the player summoning sigils.
Doing so requires items which are relatively hard to come by, at least early on in the game. Dark Souls III is probably the easiest in this regard, with a section near the end of the first ‘real’ area before the boss where you can farm a set of knights for Embers.
This next part will be a pro to some, but likely a con to many — if you’re in full humanity/enkindled state you’re much more likely to be invaded by another player. If you have summoned co-op players into your game, these odds of being invaded go up even further.
Unless you’re in a boss fight of course. Which is how co-op is generally used. Planning to play the games for full co-op in the general area play for an entire campaign is difficult.
Especially when you add in the fact that you’ll need to do every area multiple times. Everyone will need a turn at hosting to get through to the next.
Technically speaking, Remnant: From the Ashes doesn’t progress your co-op partners campaigns either. But the difference here is that you can keep them in the entire time. They get credit for everything. Get the boss drops. Get the weapons. They can come with you from start to finish in your campaign with no detriment.

With this piece — I don’t mean to put people off attempting co-op in Dark Souls.
But I think it’s important to go in eyes-open and with the right expectations. Yes. Co-op in Dark Souls is possible. Yes. It is a hell of a lot of fun, even. But know while you make the decision to try it or not that Dark Souls wants to be about the singleplayer experience first and foremost.
There is a tone- a feeling the game is striving for that it values more than multiplayer convenience.
And for what it’s worth — it’s a tone and feeling it rather successfully strikes.
Go into it — if you choose to — being forewarned that you’re playing a singleplayer experience that allows for the odd patch of limited co-op (focused heavily around boss battles, although you certainly can bring in people to help with your area clears as well) and I think you’ll have a good time.
Go in expecting a Remnant (or basically any non-Dark Souls-like title) co-op experience and that’s a path that can lead only to frustration and disappointment.