Some people note the coherence, choice of words, grammar, historical facts, science, ring theory, rulings, sharia (norms, customs which sharia is). These are qualitative aspects but again can serve in reducing the Quran,
But what most people miss out is the in-quantifiable. As Shaykh Akram pointed out brilliantly, is that it touches the "Fitrah", makes people to think and is ultimately a guidance and instruction on how to worship your Lord and how to think. The sharia norms that are closely relatd to the ones own nature (Fitrah) that are explained (similar to Jewish laws) are expounded and linked with the Creator and Worship.
What i would like to add is that it touches all types of minds since the human mind is complex and how the Quran can touch and "change" so many individuals from the lowest to the highest stratas of society in keeping them guided and straight in their focus and life. That's is why putting ones own preconceived ideas on how a text should be cannot do it justice.
Ultimately the Quran was not revealed to "impress" to "entertain" (which is how it is used nowadays).
Similarly, how remaining fragments of the "Gospels" changed the Judeo-Christian world was not by impressing, but by its in-quantifiable impact.
