Since the first time the website was introduced several years ago, Instagram has updated the design. The new design is extremely minimal, with a lot of white space and large, full-size images.
The new design gets rid of the grey textured background and the blue top bar, replacing it with a clean white everywhere. The top bar just has the Instagram logo, your account name and a logout button.
The images are now in full size, that is 640 x 640, with more space between them. You can click on an image to see the tagged people or double click to like it as before.