The level design of the original Dark souls is amazing at first glance, but the more you play it the more you realice that some sections aren't that well designed and are a pain in the ass to travel through. Like going back to Firelink shrine from Queelag's lair after defeating her. Or wasting time holding the running button in Anor londo or Lost Izalith (I understand why this happens in Anor londo, is a way of showing the player the magnificent and the amplitude of the place as the glory realm of giantesque creatures and Gods. But Lost izalith is a lost case). After getting the lord's vessel the game becomes easier to traverse, but also it becomes worse because the remaining levels are way less interesting than the first ones. In the sequels, levels become more interesting by its own thanks to losing the need of interconnect them, in a similar way to Demon's. But bonfire's placement is overall weaker in both DS2 and DS3, making the shortcuts more irrelevant than in Demon's and Dark souls, making the overall level's traverse less engaging.
That's why my favourite level design type is Demon's souls one. Each level is separate, each level is divided in sections that are connected between them, but there's only one checkpoint/warp on each section, making the exploration of the levels more interesting (if you die, you start from scratch) and the shortcuts very valuable. 1-1 from Boletaria's palace is a great example of this design philosophy.