In my opinion the best Dark Souls game.
It was my introduction to souls games so I had to learn it the hard way.
It's just an outstanding game, the bosses are pretty much all memorable (except maybe two, deacons and ancient wyvern). Even the tutorial boss, Iudex Gundyr, is a nightmare if you are a new player, it is unforgiving, fast as fuck, and makes a hell of an impression especially in his second phase that makes you shit yourself. I'll come back to write in depth about the most memorable bosses later on.
The level design I think it's pretty nice, of course it had to have a fucking swamp level that no one likes, but apart from that everything is great. I only wish that the whole world was connected like in DS1, but it is pretty close to that, the bonfire teleport system didn't bother me and I always thought it was an easy way to navigate the world, especially since it was my first time playing any Dark Souls game.
The sidequest and characters/npcs were so good that I had to complete the game many times just to get everything from them, and do the multiple endings in which you have to do really specific things with specific npcs to trigger the desired ending or you'll literally fuck everything up. Some people will probably think that it is annoying and stuff but I think it makes sense considering that you, the ashen one, doesn't really know shit about this world, you only know that some guy told you to recover some embers from some lords and you just go and kill everything in your way. It makes you feel lost as if you were the ashen one himself. Even reading item descriptions makes you wonder if what it says is true or not, it could be your own thoughts about that specific item, or what you've heard about it, and the best thing is that those items belonged to someone else previous to your arrive. So you really don't know shit.
Mechanicwise, the game is at its peak, it is fast paced, even frenetic in some fights such as Nameless King, Slave Knight Gael and Pontiff Sulyvahn, just to name some of them. The movements are fluid, the strikes are well telegraphed, and I don't recall any bullshit boss mechanic that was more on the RNG side than on the mechanic/skill side, so that's good. I think that the only "negative" thing that comes to mind writing about memorable bosses is the camera angle in the Nameless King fight (first phase), I just can't get to look at the dragon and know where the hell it is and dodge comfortably, but apart from that the fight is fucking cool and probably one of the hardest. And talking about difficult fights, there are a handful of those including the previously mentioned Slave Knight Gael, which is a fucking three phase fight, then there is Dark Eater Midir, a gigantic abyss-eating black dragon, this one really doesn't need any explanation, he's just cool and difficult. And speaking about dragons, if you thought one big black dragon was hard enough, there is also a two dragon boss, the Demon Prince, it is also a three phase fight, with two different dragons, and a third one more powerful afterwards. Then we have Sister Friede, which is arguably the hardest boss. Honorable mention to Soul of Cinder, Abyss Watchers and Twin Princess, those three are some of the coolest fights, but I don't think they are as difficult as the ones I just mentioned.
In conclusion I think Dark Souls 3 is an over the top game, it has everything it needs to be the better souls game.

Having played DS3, then DS1, and lastly DS2, it feels so out of touch with the other two. It doesn't feel like an actual dark souls game, it feels like a downgrade from DS1, and is nowhere near what DS3 ended up becoming. So it isn't even some kind of transition between DS1 and DS3, it's just another thing that in my opinion can't really relate to the souls saga.
One thing that I couldn't stand while playing it was the "difficulty meter" that DS2 tried to include, which manifest in the form of an exceeding number of enemies in a small room, that just doesn't fit with the souls filosophy of how to make games difficult. Level design maybe is not that bad, but I really didn't play too much to know and see most areas. Bosses from I could see are mostly dumb encounters and nothing really special or characteristic as in other souls. One thing that I actually liked was the power stance/dual wielding, that sadly didn't make it to DS3, but it made it to Elden Ring, and was really fun in both DS2 and ER.
To sum up, I may be bias and a little bit hater on this game, but in my playtime I couldn't really find anything that made me like the game so I just ended up uninstalling. Perhaps in the future I'll comeback, finish it, and complete all achievements as I like to do with FromSoft games.