To be honest, seeing that they aren't casting Japanese actors, Wolff does look like an American version of Light, changing the hair, his face does fit the character. That's just regarding physical aspects. He's tall, thin, and has similar facial expresions. Whether he's handsome or not is basically subjetive, and right now his timing couldn't be better given that he's the new teen heartthrob (Wolff's 20 though) thanks to precisely all these John Green adaptations and his previous role in "Stuck In Love". Regarding his acting skills, I think Wolff has a lot to offer but hasn't yet been casted to do many roles out of his comfort zone. You should look him up in Gia Coppola's Palo Alto, he wasn't the typical nerdy cute high schooler he's usually casted as, but he was a rather annoying ass kid with serious issues, and he did a pretty brilliant job. It was a sort of darker tone to the types of characters we've seen Wolff portray so far, and he managed to do it well, meaning we can't know yet whether he'll be a good Light Yagami, but I think it could work out.