The tiles take up a lot of space and have low information density. They only tell you how many messages but no preview. Web addresses pinned as tiles do not update. An app pinned as a tile for quick access is just a big ugly icon. You need a tile for each and every social media like facebook, twitter, whatsapp and every email account to get notifications. The problem is that you will soon need to scroll to look at your notifications and this is not efficient.

Overall WP7.5 does not make use of screen space efficiently. The huge oversized fonts for headings are unnecessary and idiotic. Look at the empty space under the forward arrow in the home screen, what kind of design is this?