Well, i'm a girl, so here is my say Odo
Unlike the Arwen Aragorn scenes (which for some reason bug me, though i don't know why, though it could very well be that I was obsessed with ARagorn...) Beren and Luthien shouldn't talk as much. For example...
As Beren walks through Doriath, following Luthiens voice, I think the moment he sees her (and we'll have to find one amazing actor for this) should simply look at her, and the audience will feel the overwhelming love he is feeling at that moment. Then we see Luthien, brilliantly fair with flowing dark hair and wonderous gray eyes, singing like a Nightengale. She begins to wander away, and an awe stricken Beren calls out to her, "Tinuviel" breaking the silence. She turns around, and you see in her face the same emotion that was on Beren's, yet wonder also. She looks at him, and she knows then her doom is decided. And she begins to sing to him, and they walk through the trees in complete bliss, their love blossoming as quickly as can be percieved by mortals alike.
That's what I call love at first sight. I think Tolkein does also. You see very much of him in Beren, the young tolkein at war. Alone and frightened and tired after long days of traveling and battle, then to look upon the face of the most fair maiden to ever walk the earth.How he felt, perhaps, when he met his wife the first time. We need to express that in the film.
And MOST IMPORTANTLY!!!!!!!!!!!!!!!!
This movie CANNOT be Romeo and Juliet esc. This story deserves not to be compared too. (like Twilight