Finally a good long look at a helmeted Thor and Loki...
When compared to the Loki from the comics, they've done a decent job of getting the gist of what Kirby intended. They've scaled down the horns so that it would be less trouble for the neck to hold up and easier for him to walk through doors. Note that they've left off the tassels or hair (I've always thought that it would be great if they acknowledged that it was Sif's hair that he cut from her head in the mythology, but they never have)--guess they figured that was a hard thing to portray in the film.
They've gone with a more modern version of Thor's helmet designed by Tom Raney IIRC (below) probably due to the fact that the original helmet probably tends to fly from the head of it's wearer when he moves much. Again, what works beautifully in the comics, is a bit unpractical in the real fake movie world.
Still, from all the merchandising, it appears that Thor won't be wearing the helmet much on camera anyway. Which is, for this Thor fanboy, a bit disappointing.