I upgraded to 7D Mark II, from 7D, though also by way 70D, an interim camera. My twin 7D cameras at the time, about 5 years back, replaced 1D Mark III cameras.
Love the 7D Mark II! I am so used to the very much greater AF coverage in the frame that going back to the 70D is hard, and the 7D feels primitive. The new AF system is very responsive, which is necessary for fast action fotos. My main subject is bellydancers, who move very quickly, I have to have a camera fast enough to use unconsciously.
I find the low-light high-ISO image quality about 2/3 to 1 stop better than 7D, and seem a bit cleaner than the 70D. Referring here to dark noise, mainly. I have also used all three types of cameras for astrophotography. Lunar fotos without using Cine picture styles on the 7D Mark II are as clean as with a Cine style on the 70D. I have to upgrade some software to be able to load picture styles on the new 7D Mark II. Picture styles are very powerful way to manipulate tonal response on Canon EOS cameras. Seeing the improvements on both 7D and 70D using picture styles, I now suspect a Cine picture style on the 7D Mark II will offer truly mind-blowing results.
The faster AF and frame-rate is noticeable. Other features packed in from 1D series cameras like the silent shutter mode are really important for taxim or other quiet moments in belly dance shows. The 100% viewfinder matters to me. The 7D Mark II retains all the technical capability of both 7D and 70D, plus extracts all the features I had with 1D cameras, like dual media slots.
The 7D Mark II does use more power than the 7D or 70D. All day foto shoots in the studio have more battery drain for sure, so more backup batteries are required for work. Not a huge inconvenience.
I am so satisified I'll eventually get a 2nd 7D Mark II body. I particularly like the APS-C system, the EF-S lenses are awesome, and the format is more favorable to glamour applications.
I will otherwise repurpose my 7D cameras with Magic Lantern, esp. for experimental film work, when this software is no longer in beta on the 7D.