The site is very broken if you don't have Javascript enabled. I am scared how CPU intense it would be on my mobile or cheap netbook. The details of collections don't even display any items.
Where is the list of files inside an item? Previously there was a nice table. Now everything seems to focus on images instead. IA hosts a lot of things that are not visual. Music, texts, data. Those seem like second row citizens now. The cover of an album tells me .. nothing about the music itself.
For an archive, I think this is a rather bad interface. The technical implementation seems very un-archivey and more suited to a "dumb user" discovery interface built upon an existing well-presented archive. :(
PS: The categories and tags on the side are a nice addition.
If someone from IA reads this, I think at least https://archive.org/advancedsearch.php is not using output buffering which might make user's performance much better.
Overall the site is very very slow.
edit: Some comparison images.
Old: http://i.imgur.com/gJXgJhI.png
New default: http://i.imgur.com/JOEoAiu.png
New list: http://i.imgur.com/m2d1Gf4.png