I personally spend most of my day in Outlook, reading and replying to emails, actioning tasks and organising my diary. Outlook 2013 is pretty similar to Outlook 2010 but has a new look - very white and very "tablet" in style.
You wouldn't think that removing colour from a screen would make much difference, but - in fact - it has somehow made it really tiring on the eyes to use. Other people have found the same thing and there are hundreds of posts on forums with people complaining about the same thing.
Microsoft responded by adding a couple of colour options to the final release version of Outlook 2013 but they made virtually no difference and using Outlook 2013 with my old eyes for more than an hour or so is almost painful!
There is also another change to Outlook 2013 which is a real pain and frankly bizarre. With previous versions of Outlook you could use the Windows Start menu's search box to search your emails, appointments and tasks. That's what the search box is there for? In Outlook 2013 they have removed the feature with no explanation and no way of switching it back on! Again, hundreds of people have spent time posting messages on Microsoft forums to complain and ask them for a solution with no response.
So, having persevered for 3 months, I've finally given up and switched back to Outlook 2010. What a relief. The fonts look better, the screen is clearer, I can search more easily and the whole experience is better. As a self-confessed nerd and "early adopter" I can't believe I've gone backwards and switched from Windows 8 back to Windows 7 and from Office 2013 back to Office 2010 but they are simply better products. Microsoft is losing the plot and losing ground (and sales) to Android (Google) and iOS (Apple). No wonder and it will take some real common sense and strong leadership at the top of Microsoft to turn things around.