My biggest problem with Dream Diary is Yume Nikki started out in a multitude of diverse and interesting worlds, whereas in Dream Diary three out of seven doors just inevitably leads to the sewers.
Also choosing to have those Limbo-patented action/stealthy sections that are known for being wonky despite the original game going out of its way to mostly just let you explore? Most dream inhabitants being boring shadowy creatures? The god damned forced 3d limited perspective?