Because this unification of the Roman and Greek gods has happened a little earlier than the time from which we begin to have preserved Latin texts and because the Greek gods came with a huge number of stories attached to them, unlike the Roman gods, which previously were mentioned mostly in rituals and prayers, we have extremely little information about the traditional Roman gods.
With the exception of Jupiter/Zeus, most of the Roman gods had been very different from the Greek gods who replaced them and it would have been interesting to know more about their original roles.
For instance the Roman Mars was extremely unlikely the Greek Ares. Mars was a beloved god, the most important protector of the Romans, who defended them against various kinds of bad things, like a COVID pandemy or climate change. He was not a god of war, even if his protector role meant that he could also help the Romans in wars. On the other hand, the Greek Ares was a god of destruction who was feared and hated. The Greeks sacrificed to him mostly to avoid his anger, but when they wanted help in war they usually turned to other gods, e.g. to Athena, which is why in the Iliad Athena gives some good beatings to Ares.