Designated Hero and Designated Villain: Excepting one or two members of Marsile's forces, the Saracens don't really do anything evil over the course of the story; their behaviour is in fact, nearly identical to that of Charles' forces.
Except, of course, Marsile's previous murder of Charles' ambassadors, his plotting the treachery against Roland, and Baligant's planned invasion of Charles' kingdom and the whole West.
Fridge Logic: Charlemagne is described as 200 years old. His sister's son Roland can't be more than 30. How exactly does that work?
Ho Yay: Roland's supposed to be engaged to Olivier's sister Aude, but he seems to like Olivier himself a lot more. He doesn't even think of Aude as he dies, but when Olivier dies Roland weeps and hugs his "ami's" body to his chest.
In a surprising example of a clash between early mediæval and later mediæval values, Archbishop Turpin tells Roland that a knight who is not brave, "is not worth 4 cents, and ought to be in a monastery, praying every day for our sins" — because all bishops think more highly of knights than monks, right?
After Charles convicted Ganelon of treason, not only is he sentenced to death but so are thirty of his relatives who sincerely defended him. Yup, this is an example of collective punishment where a whole family is held responsible for crimes by one member (like the story of Achan in the Bible). This is of course very unfair for modern audiences.
Back when the poem was written, it was considered the height of manliness to make a huge show of your grief, especially in battle, even to the point of falling to the ground and weeping. To modern audiences, of course, this just makes the Franks look overly dramatic.
Some modern audiences read the epic as a tragedy about how Roland's extreme hubris got him and all his friends killed. One of the translators, Robert Harrison, has argued that this sort of reading is a mistake, that Roland's death should not be read as a result of hubris, but as an event preordained by God that had to happen in order to convince Charlemagne to eliminate the threat posed by the Saracens once and for all.
Woolseyism: The Swedish translation by Frans G. Bengtsson changes the assonances to a complex rhyme scheme and adds some Scenery Porn not in the original. Some people consider it an improvement.