Well....
I really liked the SP3 form factor, as a matter of fact I loved it! But, I sold mine at a substantial loss and returned to a mid 2014 rMBP last week.
I do miss many things about the SP3 but I had bad luck with them. I believe I had a total of 4 replacements for various issues. Another reason for selling it was I just could not get the hang of Windows.. I've been a Mac user since 2008..
My main issue with Windows is at the core functions. Email, Web and Office. Email in Metro UI is a disaster in my opinion as I have no way to adjust the font size for incoming mail. I have bad eyesight, I'm old and have a very hard time reading text. IE was just okay for browsing. My issue here was I didn't like metro IE layout and UI.. Office was fine but it only works in desktop mode..
I am NOT here to slam the SP3 as I really liked many things about it. I had numerous hardware issues (maybe just bad luck) and I could never adjust to Windows. I tried for almost 3 months..
I suppose I should have held out for Windows 10 to see if that solved my UI issues but the latest hardware failure (a dead pixel dead smack in the center of the screen) pushed me over the edge..
I will keep an eye out for the SP4 as I really liked, as a matter of fact I loved the form factor.. Microsoft has a winner on their hand IF they can fix the QC problems I experienced and IF Windows 10 can solve the GUI issues..
The SP3 IS awesome.. No doubt about that! Good luck whichever direction you end up going with OP..
My .02