My progression was D200 --> D300 --> D800.
Sometimes I have reason to go back and look at my D200 jpgs (I didn't start with raw until the D300) and although they're OK, they're only OK.
I learned to shoot raw with the D300, and they are good solid images, but the D800 positively blows them away, by any measure. I've been using it for about 18 months.
Yes, the file sizes are large (mine are usually in the high 40 mb range), the body's expensive, you won't get what you paid for unless you use FX lenses (I already had two of them), it's big and heavy, but everything about it is, to me, a joy.
Live view works as you'd want it to, and it's hard for me to think about doing LV without being able to change aperture (because I almost always shoot aperture-priority). I have it on a tripod more often than not.
The exposure system is fantastic. It's rare that I adjust exposure, unless I'm after an effect. With the D200 and D300 exposure was generally OK, but the D300 would stumble sometimes. The D800, never.
I been shooting Nikon since 1965 (F --> N90s --> F5 --> D200) and the D800 is the best of the lot, by far. It lets me do any damn thing I want to, no fuss.