On the whole, while many parts of the Qur'an undoubtedly have considerable rhetorical power, even over an unbelieving reader, the book, aesthetically considered, is by no means a first-rate performance. ...let us look at some of the more extended narratives. It has already been noticed how vehement and abrupt they are where they ought to be characterized by epic repose. Indispensable links, both in expression and in the sequence of events, are often omitted, so that to understand these histories is sometimes far easier for us than for those who learned them first, because we know most of them from better sources. Along with this, there is a great deal of superfluous verbiage; and nowhere do we find a steady advance in the narration. Contrast, in these respects, "the most beautiful tale," the history of Joseph (xii.), and its glaring improprieties, with the story in Genesis, so admirably executed in spite of some slight discrepancies. Similar faults are found in the non-narrative portions of the Qur'an. The connection of ideas is extremely loose, and even the syntax betrays great awkwardness. Anancloutha are of frequent occurrence, and cannot be explained as conscious literary devices. Many sentences begin with a "when" or "on the day when," which seem to hover in the air, so that the commentators are driven to supply a "think of this" or some ellipsis. Again, there is no great literary skill evinced in the frequent and needless harping on the same words and phrases; in xviii., for example, "till that" (hatta idha) occurs no fewer than eight times. Muhammad, in short, is not in any sense a master of style.Nöldeke, Theodor. "The Qur'an," Sketches from Eastern History. Trans. J.S. Black. London: Adam and Charles Black, 1892.
The Qur’an claims for itself that it is ‘mubeen,’ or clear, but if you look at it, you will notice that every fifth sentence or so simply doesn’t make sense. Many Muslims will tell you otherwise, of course, but the fact is that a fifth of the Qur’anic text is just incomprehensible. This is what has caused the traditional anxiety regarding translation. If the Qur’an is not comprehensible, if it can’t even be understood in Arabic, then it’s not translatable into any language. That is why Muslims are afraid. Since the Qur’an claims repeatedly to be clear but is not—there is an obvious and serious contradiction. Something else must be going on.Professor Gerd R. Puin, Saarland University
"It is by no means the universal opinion of unprejudiced Arabic scholars that the literary style of the Qur'an is superior to that of all other books in the Arabic language. Some doubt whether in eloquence and poetry it surpasses the Mu'allaqat by Imraul Quais, or the Maqamat of Hariri, though in Muslim lands few people are courageous enough to express such an opinion."
C.G. Pfander, The Mizanu'l Haqq ( Balance of Truth') p.264
"When we read the Old Testament in the original Hebrew, many scholars hold that the eloquence of Isaiah, Deuteronomy, and many of the Psalms, for instance, is greater than that of any part of the Qur'an. Hardly anyone but a Muslim would deny this, and probably no Muslim who knew both Arabic and Hebrew well would be able to deny it."C.G. Pfander, The Mizanu'l Haqq ( Balance of Truth') p.266