The difference between the violent passages in the Koran and those in the Old Testament (as more comprehensively explained here) is this: the Old Testament is clearly describing historic episodes whereas the Koran, while also developed within a historical context, uses generic, open-ended language that transcends time and space, inciting believers to attack and slay nonbelievers today no less than yesterday.
Thus in the Old Testament God commands the Hebrews to fight and kill "Hittites," "Amorites," "Canaanites," "Perizzites," "Hivites," and "Jebusites"—all specific peoples rooted to a specific time and place; all specific peoples that have not existed for millennia. At no time did God give an open-ended command for the Hebrews, and by extension their Jewish descendants, to fight and kill all "unbelievers."
To be sure, Muslims argue that the verses of the Koran also deal with temporal, historical opponents, including the polytheists of Mecca, and to a lesser extent, the Byzantine and Sassanian empires.
The problem, however, is that rarely if ever does the Koran specify who its antagonists are the way the Old Testament does. Instead, Muslims were (and are) commanded to fight the "People of the Book," which Islamic exegesis interprets as people with scriptures, namely, Christians and Jews—"until they pay the jizya with willing submissiveness and feel themselves utterly subdued" (9:29) and to "slay the idolaters wherever you find them" (9:5).
The two Arabic conjunctions "until" (hata) and "wherever" (haythu) demonstrate the perpetual and ubiquitous nature of these commandments: There are still "People of the Book" who have yet to "feel themselves utterly subdued" (especially all throughout the Americas, Europe, and Israel) and "idolaters" to be slain "wherever" one looks (especially Asia and sub-Saharan Africa).
In fact, the salient feature of almost all of the violent commandments in Islamic scriptures is their open-ended and generic nature: "Fight them until there is no more chaos and [all] religion belongs to Allah" (Koran 8:39).
This fact will ensure that as long as the Koran proliferates and is read as God's literal word, its readers will continue to exist in a dichotomized world, themselves versus the rest.