Outlook Caviat
I made the jump from Office 2010 to Office365 which includes Outlook 2013. Generally, if you were happy with 2010 you'll be happy with 2013. From a technical point of view it seems to be more stable and a bit quicker... but that's just a subjective opinion based on my hardware.
You mentioned that the Calendar portion of OL was key to you, this is why I jumped in... As an FYI they nerfed the "upcoming appointments" preview in the To-Do bar. It now only shows the current day with no overview of the next day. For me this has been an inconvenience as I don't normally have many appoints on my calendar so this was a handy reminder for upcoming events. Now I have the added step of physically having to review my calendar in "month view" to see what's coming up.
If you do a web search, you'll find many features have been removed from Office 2013 in general, most were obscure, outdated and rarely used features but i'm sure for some people they could be quite significant.
Also if you're using the "touch" features of Windows 8, there is a touch-mode in office (makes the main menu buttons bigger) but as a whole the suite is not very touch friendly and you still really need a mouse and keyboard to have any degree of productivity. - Pf
