First, of course, there's the overly didactic tone, the repetitive nature of the text and the generally bad writing (as that poor Arab pagan poet, who took the Qur'anic challenge to "write something as good as this" at face value and was executed for succeeding, found out to his chagrin; sadly, it is extremely easy to surpass the Qur'an in literary quality, regardless of the language used).

Second, every fourth phrase or so makes virtually no sense in the original Arabic because it has probably been wrongly marked. In that, both the original Arabic and the translation are going to mislead you because the one reflects attempts by later writers to interpret something and the other sanitizes meaningless statements to make it sound as though they make sense.

The Qur'an is in need of serious academic criticism and study, leading ultimately to massive revision, but of course it is difficult to actually do that without getting death threats from crazies.