What is a dominant theme in Book One of Ovid's Metamorphoses that could be used for a presentation?

One of the themes you might wish to discuss is the utter amorality of the gods. It's important at the outset to understand the difference between immorality and amorality. Immoral actions are those that depart from an established set of norms or conventions. Amoral behavior, on the other hand, shows a complete indifference to any system of morality whatsoever. And this is how the gods behave, which is not surprising when you consider that they can do pretty much as they please. They're gods, so who's going to stop them from doing what they like?
Although Ovid calls on the gods for inspiration, he doesn't paint a particularly flattering portrait of them. In Book One of the Metamorphoses, for example, Apollo falls head over heels in lust with the nymph Daphne. He's so overcome with desire that he tries to rape her. It takes a sudden intervention from her father, Peneus, to save her honor. He turns Daphne into a laurel bush and Apollo is left frustrated.
But the other gods are no better. Jupiter—the equivalent of Zeus in Roman mythology—rapes Io, another unfortunate nymph. As he's the father of the gods there's no one to stop him from doing whatever he likes. Although he later takes pity on Io, Jupiter only does so to allay his wife Juno's suspicions. So even actions by the gods that appear on the face of it to be noble and just are motivated by self-interest.
The gods' amorality comes through most strongly in their relationship with mortals. In Book One an angry Jupiter punishes humanity with a flood, and all because of a negative experience with just one man, Lycaon. As this episode clearly demonstrates, the gods are very sensitive to even the slightest hint of disrespect from humans, and woe betide anyone who dares to anger them or defy them in any way. The only mortals who survive Jupiter's mighty flood are Deucalion and Pyrrha and that was only because they'd paid appropriate piety and respect to the gods. Burning incense and making animal sacrifices are considered more important to the immortals than the virtual annihilation of humanity.