The level design in DS2 was great. It wasn't like DS1, however, which is why everyone complains about it. Think about it, every transition path/elevator/tunnel between areas is actually just a fast-forwarded representation of days or possibly weeks of travel time. We're talking about that huge map in the mansion's basement, where you're traversing the entire kingdom through your journey, lighting primal bonfires at the far edges. And the DLCs took place in other kingdoms entirely! Of course when you don't have a level layout where every area intersects every other area you don't have the shortcut porn that DS1 has. That layout is really just another bit that DS2 took from Demon's Souls (along with hollowing reducing max health, a ring to counter said health loss, consumable healing items, talking to an NPC to level up ... ).
DS1's layout is the one that really made little sense. Other than obvious jump cuts to distant areas, the main game is one small area probably no more than 1 mile in diameter, because you can literally walk from one side to the other in far less than an hour (ignoring enemies) even though it's a windy path. I mean, DS1 could fit almost entirely within about a 20 x 20 city block square. That is much smaller than the game makes you think it is.
DS2 was bad. 40% of the game was behind one switch on one tile that looked like a light. Tons of mechanics were broken: no dead NPCs, no ladders, etc I beat the whole thing with 100% slow completionism (50hours) like the dev's imagined and then realized that the death->broken right was back there. I didn't have the hear to go through the whole game again. It's like they just threw out the wonderful level design of DS1 "because warpz" and then wondered why people call DS2 the black sheep.
I'm going to have to disagree with you. NPCs could indeed die (and if you mean hollowed NPCs, no there weren't 'stories' for the NPCs where you help them and they hollow out on you, but that's fine, it shouldn't be trying to copy the first game in every detail), there were lots of ladders (you could buy some from an NPC!). Powerstance actually worked to make dual wielding actually good! The paths branched out and could be tackled in several different orders, though they did put some blockers in place to actually keep people from losing track of all the available path options. Because the land is huge and sprawling, bonfires are all teleportation points, simply to save you time, otherwise everyone would be bitching about how far you have to keep backtracking. The ability to speed climb ladders, as well as the ability to slide down or just drop off were great additions. The ability to roll in more directions, especially while locked on, was a huge improvement.
Yes, it definitely has some weaknesses. Fall damage was worsened when it should not have been. There should have been more bosses and enemy types that weren't humanoid. Dex weapons were nerfed a little too much. You can't make a proper left-handed character (DS1 is still a far worse offender, however). Arguably, the DLC bonus areas, which are DESIGNED FOR SUMMONING FRIENDS, absolutely suck to try and solo your way through, but at least you can either just skip them entirely, call in allies (they give you NPC summon signs, just in case), or try to be a badass and attempt to solo.
I guess, ultimately, DS2 is more a spiritual sequel to Demon's Souls than it is a proper sequel to DS1. And anyone who doesn't like (or never played) Demon's Souls, or vastly prefers DS1 over it, won't like DS2 nearly as much because of that.