It's interesting to see Light without his memories, because it gives us some insight into what he was like before the Death Note.
I think Light has always seen himself as above other people, but it seems like he didn't develop his intense impatience and scorn for everyone else until he was given the power of the Death Note. Getting the power to decide whether people live or die very seriously warped his view of others. He's a god to them; what are they worth? They're targets, they're obstacles or they're insignificant.
It's particularly interesting to see how the amnesiac Light interacts with Misa. He finds her frustrating - she decided she was in love with him and now she won't leave him alone - but he still views her as a person. He's concerned for her safety. He's direct with her, but he's never cruel.
The amnesiac Light point-blank refuses to exploit Misa's feelings for him for information. Light thinks of himself as fiercely principled, which, paradoxically, is part of the reason he ends up killing so many people. When he kills to test out the Death Note, he's so shaken by having broken his principles that he has to retroactively rewrite those principles in order to convince himself that his murders are morally good.
This is an aspect of Light I find really interesting, and seeing him without his memories really helps to bring it into focus. If you see the world in black and white, if everyone is good or bad, it's easy to tell yourself that you're a good person and therefore your actions are necessarily good. Light isn't a bad person, so how could the things he's done be bad? Someone has to clean up the world, and he's the only one who can.
I love it when Light, without his memories, finds himself worrying about whether he could be Kira. Whether, if he had that power, he'd use it to kill. He knows he believes that some people deserve to die, and that worries him; is he really the sort of person who would be prepared to kill them himself?
I wonder what the amnesiac Light would have done if he'd managed to deduce that he actually was Kira, rather than getting his memories back before he had the chance.
I feel so sorry for Light when he has amnesia. Just a bewildered, suffering piece in his own game. Light will use anyone as a pawn, himself included. He gets himself imprisoned for at least fifty days, and for over forty of those days he thinks he's innocent and being framed.
And then he's handcuffed to L for over two months, which is just hilarious. What a sitcom premise. They must have got to know each other so intimately, or at least as intimately as you can when one of you is extremely private and the other has significant parts of his memory missing, which is still more intimately than they're used to knowing anyone.
I like to think that L sleeps in absolutely ludicrous positions, which is really disconcerting for Light when they're handcuffed together and have to share a bed. Light keeps waking up to find L sprawled across his waist, or kneeling with his face in the pillow, or sleeping with his legs on the bed and his head on the floor.