Ummm....
TOTALLY avoiding the 20th c., I think we're a bit too grown up here to be repeating MEDIEVAL propaganda, aren't we? These are the same folks who claimed Jews sacrifice and eat babies.
The Ottomans did occasionally massacre PoWs, as did the Christians. They did not massacre civilians, except those that died as the result of the sack of cities that did not surrender, as opposed to Christian armies, that raped and pillaged everywhere they went (4th Crusade, anyone?). Ottoman troops were executed on the spot for taking anything from peasants without compensation. The most famous massacre of PoWs occured after the battle of Nikopolis, when Bayazid massacred the PoWs in retaliation for the Crusader's massacre of the Muslims of Nicopolis; however the nobles were ransomed (Duh). And interestingly, in a battle that was a pretty close call, the Serbs remained on the Ottoman side, prefering the Sultan rule to Hungary. The mere fact that Muslims were not allowed alchohol would have made a very large difference in the behaviour of an Ottoman army vs. a Christian (not to mention military performance).
The Ottoman tax load was a fraction of what your typical Christian peasant faced, subject to feudal dues instead of the needs of a centralized government, and its hard to argue that the Ottomans were anything but the most religiously tolerant regime in the European world - their rise coincided with the horrific wars of religion wracking Europe, and the Jews of Istanbul are the direct decendants of those expelled from Spain by Ferdinand and Isabella. Ottoman success was not just due to military superiority, but also organizational superiority and the desirability of Ottoman rule vice the rapacious rule of Feudal nobles. If you have ever read an account of the Hundred Years War, you would know what a huge problem the armies of mercenaries roaming around destroying everything were.