(No, they didn't give me one.) If it's not everything you think it should be, you probably don't understand reality.
This was a good surprise (and makes me think less about the D400 and D7100). A reasonable resolution from the sensor, plus good low light performance (technically, so far to ISO 12800 within the suggested range), and an auto focus unit that goes almost as low as the Panasonic GH3/GH4, to EV-3 gives this camera body a lot of appeal for a reasonably low price.
You can say that Sony has something smaller and cheaper, but if you want great performance, you don't go to Sony yet. I'm not saying that the Nikon D600 or D610 are great but it seems that we'll get great performance from the D750 that sports photographers would love--something that didn't quite make it all the way into the D800/D810.
The Expeed 4 processor seems to help quite a lot. It's showing up everywhere now, and it feels as though Nikon has smacked Canon up one side and down the other, even as a replacement for the 7D is around the corner.
Is US$2299.99 a huge price? I don't think so when you compare what else is available, even if you just look at Nikon's products.
I wonder if the use of polycarbonate will compromise the weather-proofing of the D750 body. It's certainly a possibility for damage during a drop. The lighter weight should be useful, though, as long as the balance with the 70-200mm f/2.8 lens is still good.
Why is this important? That would be my main combination, especially for sports. I'm betting for a lot of those with the D700, it's an easy switch. Handling the file size will be the real problem, going from 12 MP to 24 MP should be a bit troubling but no more than going from 6.x MP to 12 MP, right? Big cards are required.
I'm guessing that the pre-orders are going to be excessive.
(Oh, I've seen some comments that seem as though Nikon has done a terrible thing--that the D750 cannot be the replacement for the D700, emotionally or otherwise. If I look at camera bodies as more than tools, I would have to say that the Olympus OM-1N was the best 135 Format film camera body ever created. It was good, but I don't believe that it was the best. Life goes on. We'll survive the changes.)
Update 2014.10.15: I handled a D750 at Best Buy yesterday. It was not as heavy or large as I expected, definitely smaller than the D810. That said, you'll probably find it heavy and large. I still like my dSLRs. It felt as though it would be well balanced with any 70-200mm f/2.8 lens, though they had something of a normal zoom mounted that brought up the price another US$700.
Update 2014.12.17: I still don't understand the emotional backlash. The body seems to be everything that it needs to be, at a reasonable price. Some of the bundles are consumer-oriented but then, the body is almost as consumer-oriented as the poor D610 with the D7000's I-guess-I-got-it AF but impressive as a semi-professional model instead.
Update 2015.01.01: There seems to be a problem with flare in certain D750 bodies. It's worse with some lenses than others, apparently. Take a look at The Imaging Resource's article in the link.
Update 2015.03.22: Seeing the DPReview review, I've been surprised about the results. It seems the image noise is lower than that of the Canon 5D Mk III, and that's impressive. Even though the D750 is a bit less rugged, it's also lighter and smaller.
Update 2015.04.08: Having photographed a scooter competition at the indoor skate park of Woodward West recently, I'm seeing the need for better image quality at ISO 3200. I'm not exactly what will work for me, but the D750 seems a good fit. The Tamron 15-30mm f/2.8 lens also seems good for me, as it is weather-sealed. The limited 2x zoom may be a bit wide in contrast to my 135 Format effective 24-80mm f/2.8 that I use regularly--24-70mm f/2.8 would probably work better, but the pricing may be too much.