It would be great if we could have an option to use the old-style sitemap with everything on the left, instead of being forced to use the top-navigation.

Existing customers from CRM 4.0 and 2011 upgrading to 2013 are going to be faced with a completely new UI, and some users just want the experience they're used to.

Personally, I like the new navigation, I just think giving customers the option to keep their existing sitemap might make the upgrade process a bit smoother for them, without introducing too many new things at once.