With Dialogue, abilities, quests, items etc. One thing I noticed recently is if you're an elf, Paarthurnax will say, "Greet me not as elf, but as Dovah!" If you're a human race, the word elf is replaced with mortal. I noticed this only now because I never played that far into the MQ as a Mer.
I also liked how early in the MQ Farengar wonders if a dragon could be captured alive, and then later...well...you know.