My fourth DSLR.
It was the direct successor to D100.
For me, it replaced my D100 and D70, my first and second DSLR (D70 which supposedly replaced my D100 showed CHR Errors, so I had to revert to D100).
D200 was released at a turbulent period when cameras were making a transition from film to digital.
Before D200, a camera meant film; digital cameras required the prefix 'digital' to differentiate from conventional cameras.
Up until D200, DSLRs were designed around a film camera, and were based on lower-grade models to reduce cost. So DSLRs at that time were sufficient as 'digital cameras' but questionable in quality when simply views as 'cameras' (film cameras of similar price range were notably better in quality).
From D200, Nikon (and other manufacturers) started designing DSLRs specifically as digital cameras, with no film camera equivalent. As a result, quality of DSLRs matched that of film cameras of similar price range.
Since then, 'cameras' meant digital, and conventional cameras were fitted with the prefix 'film'.
Compared to predecessor D100, D200 was miles ahead in terms of build quality, with magnesium alloy body, and heft to match. Controls were upgraded from D100 as well. Where D100 controls were similar to F80, an upper entry-level film camera, D200 controls were similar to F100, enthusiast-level film camera.
Image sensor was upgraded to 10 MP, with faster burst. Down side for better sensor was lower battery life. This was a sour spot for me, since I greatly appreciated D100/D70's near limitless battery life (major reason why I chose D100 in the first place).
D200 also was a turning point for Nikon in terms of image output. Previous Nikon DSLRs opted restrained colors, which was welcomed by those who wanted realistic images. But vivid color rendition offered by rival Canon was better received by most consumers. Nikon had no choice but to answer to consumer demand, so D200's color rendition was shockingly vivid at default setting. This trend was balanced out in succeeding D300.
D200 shows signs of age when it comes to features. It has no sensor cleaning mechanism, so one has to be very careful when switching lenses. Rear screen is microscopic by current standards, and limited in resolution.
D200 may not be the ultimate DSLR as it once was, but I still find it a very capable camera, more comfortable to use than many later DSLRs that have come and gone since.