I bought a new Nikon D800 right when it came out, and I used it for well over a year. It’s a great camera!
I used to have a Nikon D3X and many people wonder why I would rather have the D800. One reason is the megapixels and cost. Both are better! I know people often groan at the megapixel bit, but I do like having very large images. Given the choice of a medium or high-res photo, I will always take high-res. It’s not for prints, although that helps — it’s also for monitors and wall-displays of the future. Another significant reason is that it is better in low-light. It will shoot at 6,400 ISO instead of 1,600 ISO. Some minor points that make it better for me are: It is cheaper, it is smaller and lighter, and it has a bigger screen (3.2″). There are many more advantages, although very minor.
These include a self-cleaning sensor (hope it works!), a quicker shutter lag (119 ms faster!), video (which I won’t use too much, but happy it is there), and it is over twice as fast to start up.
The Nikon D800 is the world's highest technical performance DSLR for outdoor, nature, landscape and many other kinds of precision photography. The D800 is the biggest news from Nikon since 2008 when they introduced their last all-new full-frame DSLR, the D700.
The Nikon D800 is the world's best for these things because it has such extremely high image quality that it exceeds not just every other full-frame DSLR ever made, it also replaces medium-format digital cameras that cost as much as a new Mercedes.
The D800's image quality is unexcelled, and it weighs less than any other Nikon full-frame digital camera ever made, making it unquestionably the best DSLR to carry when you have to carry a DSLR in the field.
The D800 has more resolution than any other full-frame DSLR by a large margin, more than twice as many pixels as Nikon's own brand-new professional Nikon D4 that sells for twice the price!