Over consumption: Siddhartha lives a life of modesty and does everything to the smallest degree that it can be accomplished for most of the book. If Siddhartha were to see current western culture he would likely be sickened by how much we consume and how unfulfilled we act.
Siddhartha would likely see most of our culture to be greedy. We run off of things that are completely non essential to human survival like coffee and a lot of medication.
Siddhartha would likely consider westerners as a whole to be disrespectful to nature. This would not be entirely because we destroy a lot of it but also because we do not value it.
Western culture is mostly run off of a tight schedule and there are deadlines to be met at every turn. Siddhartha does not live like that at any stage of his life, even as a merchant he has no interest in being productive very quickly.
Siddhartha lives his life first as a Buddhist and follower of the path to attain enlightenment. Western culture as a whole is diverse in religion and spirituality but the majority of the people will live a life first and foremost and their religion comes second or third.