I think that gameplay wise RO2:HOS can be one of the greatest games ever made and a lot of the things needed are probably not more than changing some numbers in the config files. But at the moment how everything plays together just hasn't gotten "it". Initially I liked the additional speed to go to iron sight, but that is a first impression, and I think that a lot of RO2's settings are features are set so that as individual features they feel the best, but things just don't work together in the same magical way as in the mod or roost.
Zets has nailed it, as always.
What made RO:OST work was a very fine balance between lots of different mechanics. There was no one thing that made RO work.
However while RO:OSTs was missing many useful features (mantling, breaking reloads etc), the core gameplay and balance (asymmetrical balance i might add) was sound.
RO2 has the reverse problem. Most of the features are inherently better (weapon collision, mantling, weapon breaks, fluid movement), however, lots of little details have been changed, that when combine together simply don't form the same gameplay experience.
RO2 simply feels less real, less immersive, less intense than RO1, which is what I played it for. Death has little meaning in RO2, but RO1 produced fear of death like no other game (partly due to immersion, partly due to slower pace of game).
For all its faults, RO was always eminently playable, and "RO moments" where frequent due to the fine gameplay balance. In RO2 I have only had 1 such moment in all my playing, and the balance and reduced immersion is a big part of it.
Many decisions have been made to make the game more fluid and accessible, at the expense of experience. Some of the most intense moments I had in RO1 where when my weapon was shot out of hand (a feature now sadly gone). Suddenly your whole game changes, in a second you go from fighting to running and hiding, looking to get your hands on a weapon.
There are many other such changes that on the face of it simply make the game more "fun" and accessible, but a really removing important gameplay experiences.