I have been using Nikon equipment since I was a kid. My first digital Nikon was a D-90. I really like the camera and still have it. I stepped up to a D-7200 a short while ago and thought I would tell you what I think about the new camera. Now to put things in perspective I am not a professional photographer I do this for my own joy.
I love the hand feel of the D-90 so when I picked up the 7200 it felt pretty much the same in the hand. The controls are slightly different but fall pretty much into the same area. The menu system is almost the same but the 7200 has a few different settings. The 7200 had dual card slots and this is a huge upgrade over the D-90. The slots allow for several different configurations and I’m not going to go into great detail on how they can be setup. I use RAW on both with JPEG on one. Don’t know if that is the best way to use them but it is how I set it up.
The one huge difference between the two is buffer speed. 7200 is so far superior over the D90 it just amazes me. Change the cards to JPEG and the 7200 can flat out take pic after pic with no lag (I have identical fast cards in the dual slots). The D90 will sometime just lag and I was use to it so I never really noticed it. Now I do.
The 7200 with the same lens focuses faster and more consistently. The 90 will “hunt” sometimes and again it was what I was use to it. Picture quality is more down to personal preference. To me in RAW the 7200 captures a better pic to post process. The best way to describe my D90 is it takes a picture closer to a film capture than vs the 7200 that captures a better digital pic. Basically put the D90 for me I could pretty much take the pictures and without post processing hand them to friends and family and they loved them. The 7200 gives me greater flexibility in post processing and that is huge because that allows me to process the pic the way I not only see it in my mind but also my artistic side.
I do prefer the button/dials/switch setup on the 7200. Just easier to do on the fly. Hate the battery charger that comes with the 7200. Just a bad design and really poorly designed to take with you. Better get an extra batter because the charger takes up way too much room.
I could break down the ISO differences ..the white balance difference..etc but in day to day shooting the D90 worked perfectly.
The wifi part of the 7200 I have played with but really don’t use it because it is quicker to pull the card and put the pics on my laptop than trying to do so wirelessly. Using the app on my phone to shoot pics…the remote is a far better option.
If any of you are considering the move from the D90 to the 7200 I can say I really do like the 7200. Once using it I can really tell the age of the D90. They both take great pics, but the 7200 gives me more to work with in the end. If you are not into post processing then the D90 is perfect if you like to have a better palette to work with the 7200 is superior.
Just my opinion and the pros can tell you way more than I could every tell you.

I just jumped in the deep-end, for the first time, and ordered a D7100 refurb body to, not replace, but supplement my FE2 film body. Never had a digital that wasn’t a pocket point-and-shoot, so I’ve got a learning curve ahead. Example: I know nothing about “white balance”.

I went for the D7100 as the deal I got on Amazon (through Adorama) was about the same as a D90 body would have been, and about $600 less than a D7200. Would have loved the better buffer on the D7200, but I didn’t think that it was worth that much more to me to have, considering my previous “buffer” on the FE2 was my right thumb. 3 fps, tops! So, the D7100 will be like stepping out of a Sopwith Camel and into an F15E.