I do not understand why dark souls fans get so... cranky when someone dares to criticize DS1 in any way. Not liking parts of it is legitimate.
It has fine level design in the first half - some of it is even great. But it's not the BEST LEVEL DESIGN OBJECTIVELY EVER. To be honest, compared to good old Ultima Underworld 2, it loses a bit in level design, and I definitely like DS3 and Bloodborne better as well.
But poor? Only a few areas are really poor in DS1, likely due to being rushed. Lost Izalith, Crystal caves, yeah, those are poor. Some are meh, like the tomb of giants (died only once in it, in the "trap" dark room with the ton of skellies, overall just very meh with the lack of light) or the forest. Others are really great, like the whole interconnected Undead Burg -> Depths -> etc and of course Sen's Fortress, the not!Zelda level.