I think that much of your opening is going to be based on what you will be arguing in the paper. Without this specification, the introduction is going to be a challenge. On one hand, I think that any introduction to a paper comparing Homer's work to the film would talk about how there have not been that many cinematic versions of The Iliad. It might be an intriguing opening to talk about how few cinematic renderings there are. This might be due to the fact that the Iliad is much more challenging to hold on to from an intellectual and dramatic point of view than its counterpart, The Odyssey. Homer seeks to bring out much more in way of complexity and intricacy in the Iliad, perhaps contributing to why there are not that many versions of the film. (It might be here where I think that using some evidence from the editors of the film would be helpful, who argued that the choices that emerged pitted them against book and film with them choosing film over literary work.) This might also assist in setting up how the film's significance is more in its endeavor and attempt than in the actual product. From this point, I think that the development of the thesis, what you are exactly going to be arguing in the paper, is going to determine how the introduction will be formed. Develop this idea, first and all else will flow from it. In this light, your choices might be to argue that the film represents the literary work well or lacks a full ability to represent the divergence of the work. In determining what the thesis statement will be, an introduction and starting off of the paper can be more defined and focused.