No, it's not an "outstanding lens." It's a very good lens
for its extreme focal range. At 18mm, it's very sharp, but at the 200mm end the sharpness rolls off pretty quickly- and the 4.1% distortion at the 18mm end is very heavy- in fact it appears to be the distortion king of any rectilinear Nikkor lens.
The MTFs are for DX- look at resolution out past about 7mm from center:
http://imaging.nikon.com/products/i.../dx/af-s_dx_18-200mmf_35-56g_ed_vr2/index.htm
Now, compare that to the 70-200mm at 200mm which is a flat line out past the edge of the DX frame:
http://imaging.nikon.com/products/imaging/lineup/lens/af/zoom/af-s_vr_zoom70-200mmf_28g_if/index.htm
One of these two lenses is
outstanding at 200mm, and it's not the first one.
The newer 70-200 VR2 gives up some sharpness in exchange for vignetting control:
http://imaging.nikon.com/products/imaging/lineup/lens/af/zoom/af-s_70-200mmf_28g_vr2/index.htm
It's
still sharper than the 18-200 out to the edge of the DX frame. Note that at 200mm, the 18-200 is stopped down to f/5.6- if you stop down pretty-much any of the constant aperture Nikkor zooms to f/5.6, they'll be sharper than the 18-200, their MTFs are for f/2.8
If you look at a professional lens like the 70-200mm compared to the 18-200 consumer zoom, here's what you'll see in Photozone's resolution tests:
18-200mm resolution @200mm:
Aperture Center Border
f/5.6 1945.5 1724.5
f/8 2010 1730.5
f/11 1880.5 1706
70-200 (VR-I) resolution @200mm:
f/2.8 3366 3194
f/4.0 3815 3376
f/5.6 3935 3284
f/8 3775 3221
f/11 3613 3102
When you consider the DX vs FX differences, it's pretty clear that the 18-200 has a ways to go to be considered professional quality glass- in fact almost twice as far.
Very few professional photographers shoot with variable aperture lenses mostly because they're too slow to shoot in most conditions, and they don't offer enough depth of field control under those conditions. A super-zoom like the 18-200 is a lens of convenience for travelers and those who don't want to change their lenses in a variety of shooting conditions- that's not normally a professional photographer trait.
Paul