I don't know what I did right in my life to be treated so well by the staff at my local camera store, but THANK YOU UNIVERSE, it is awesome. There was a release party last night, with several D750 bodies to demo. I spent no less than an hour shooting various lenses with it, I forgot an SD card and the NPS rep gave me one. Seriously?! They are awesome.
So now I've shot with the D3000, D50, D90, D600, D700, D750, D800 and Df. The D700 & D800 are the only two bodies that were marketed as pro bodies, and are the two I currently own.
A quick run down -
Smaller, lighter, thinner than even the D610. I say this, but I don't feel like it felt cheap in my hand, or like a toy. I did feel this way a little about the D600. The D750 is the first Nikon body to use carbon fiber in the build. The grip is nice & deep, so you've got a good handle in it when you hold it.
Redesigned 24 MP sensor. Nikon sensors are amazing, so I don't really need to go into this much, but the file size is perfect - not too big, not too small. The reports aren't out yet on how the color depth or dynamic range compare to the D810, D610, D4s, but if I'm guessing... It's probably the same or better than the D610 and not quite as good as the D810.
Auto focus is quick, accurate, and quiet. Shutter is quieter too. The AF system is the new Advanced Multi-CAM 3500 II - an improved version of the stellar AF system in the D810 & D4s. Yes, improved. The other two bodies can focus scenes up to -2EV, this one can focus up to -3EV. Basically, it can see & focus in the near dark.
Expeed 4 image processor - same as in the D810.
It has a one stop high ISO advantage over the D610 (Native 100-12,800), and I've seen an image at 51,200 ISO and it looks incredible. Completely usable.
Dual SD card slots - no CF cards. Initially this bothered me, but not anymore. SD cards are lighter, cheaper and nearly as fast. I'm going to stop resisting that they are the way of the future.
The D750 is also the FIRST Nikon FX body to have a tilting/articulating LCD screen. I handled it, and it's definitely well built. No worries about breaking it, honestly, it seems pretty dang durable!
Speaking of the LCD - bright & clear. If I'm not mistaken it's the same one as in the D810 and you can color calibrate it.
You can preview exposure in Live View! (You do have to turn Exposure Preview to "On" in the menu, however.)
With this AF system and sensor, this camera will have no problem producing incredible, professional images. I expect it to outperform most bodies in low light performance, save the Df and the D4s.
Nikon is marketing this as an "enthusiast" camera body, the same way they did the D600/D610.
The main differences I see between this body and my two "Pro" bodies, is the button layout. On my D700 & D800 my ISO, WB, Qual buttons are all on the top, right under my left pointer finger. On the consumer/enthusiast bodies, they are in the back to the left of the LCD. Still easily accessible with the thumb.
•No AF-On button. Damnit Nikon! The AE-L/AF-L button can be set to use as AF-ON and works perfectly. It's a little farther reach but in use, I really didn't notice.
•Sync speed 1/200 (D700 & D800 are 1/250) (Point to consider: Plenty of people consider the 5D Mark III the "ultimate wedding camera" and it has a max sync speed of 1/200. Nobody seems to have a problem).
•Max shutter speed 1/4000 (D700 & D800 go up to 1/8000) (Point to consider: If you're coming from a D700, you will lose a stop on the high end of the shutter speed, but GAIN a stop on the lowest native ISO. D700 at ISO 200 and 1/8000 would yield the same exposure as D750 at ISO 100 and 1/4000, so if you haven't had any issue with the D700 I wouldn't worry about it with the D750.)
That's pretty much it! If I missed anything or you have any questions, please chime in below via the comments!
NIKON D750 ISO COMPARISON (via 246-You on Flickr):
OTHER SAMPLE IMAGES FROM THE NIKON D750 (Various photographers; click each image to open in their Flickr stream):