An addicting experience to say the least. While the worldbuilding and level design will never exceed that of the first game, it still manages to stand out in its own way. The callbacks to the original are fantastic, building upon the lore of the first game and wrapping it all up with a nice little bow. It looks fantastic (I usually never take screenshots of games I play but this one earned an entire album on my Steam profile). Its combat is improved, being tighter and more fluid than the first game's. The ability to warp between bonfires from the get go is really convenient. Weapon modification is drastically improved, as well as the overall UI. Disappointing to see the armor modifications go, though. Estus Shards and Undead Bone Shards are a much better way to level Estus than kindling in the first game. Armor has a ton of variety but unless you're wearing Havel's set or the Catarina set, physical damage reduction between sets isn't really noticeable (I don't play magic builds, I'm either a strength build or a dex build). Boss fights are exhilerating and really well designed. The soundtrack has more overall memorable tracks than the first, but it's not like I'm going to forget the Firelink Shrine theme or the O&S theme anytime soon.
The story is incredible. You're not going to get much of it just from the game, so I recommend VaatiVidya's videos on the lore, but wow. What a story. This is easily one of the best games I have played in recent years.