Avengers concept art: Charlie Wen and Ryan Meinerding

Charlie Wren's designs for these characters in the Avengers was a minimal change but subtlety better.

“For Thor, I was trying to come up with something that at first glance felt much like the original Thor film, but transitioned a little closer towards Odin’s warmer metals to show his growth from the first film.” -  Visual Development Supervisor Charlie Wen.  Page 138.

I don't see this 'warmth' that closely, as they appear to be silver in both films, and if anything his costume gets more blue. Perhaps this refers to patters, which would make more sense. I do think the trousers have improved with the red rim running down them, and I also prefer the patterns on the chest piece ans they have a more memorable and iconic impact.

Loki's costumes are also very good, thou they bare a very similar appearance to his look in Thor, but his coat seems much longer, this gives him a somewhat more traveled look. I think the armour is also much improved, is more spread around his whole costume and less cramped in the torso.

I like the idea of the green cape too, it makes him look more like an equivalent villain to Thor, but in comparison to the less armoured look I am in favour of the lesser armoured appearance.