Where gmail still has an advantage over outlook.com is this consistency in branding. Hotmail, msn live and now outlook branding is just confusing. Outlook is much cleaner but gmail still has more functionality and a more transparent layer of integration (like calling a phone number directly from your list of friends on the left) while outlook either doesn't offer these features or if it does, it's a whole separate page/interface. Try Calendar for example from the top drop-down.
(* you not: As I am typing this (9:37 am PST), gmail wouldn't load while outlook.com does)