Bob Johnson at Earthbound Light looks at Nikon Capture NX in Hands On and Second Thoughts:

So, what's my verdict on Capture NX? I must say I have developed a deeper appreciation for what Nikon and Nik Software set out to create, but I'm not sure it's for me. My workflow revolves around Photoshop and I don't see that changing because of NX. I'd highly recommend though that digital shooters who are not Photoshop fans take a good look at Capture NX. This may just be what they've been looking for.

It's interesting that Bob's main comparison is with Photoshop. Capture NX clearly isn't as fully-featured as Photoshop but it does offer a simpler way to do a lot of image editing, even if its rendering speed appears much slower.

In focussing on editing tools, I wonder if its designers (as well as Bob) took their eye off the program's other main use: bulk processing raw files, fixing white balance, tweaking their exposure and making other global adjustments to multiple files. Such adjustment work is so much quicker in NX's existing competitors like Adobe Camera Raw which (once Bridge's cache has built) is an easy matter of copying and pasting settings. Instead in NK there's a long wait while it rebuilds the raw file. So NX still needs work - and I'm not even comparing it with its newer competitors like Aperture and Lightroom.

See Nikonians discussions on Capture NX and this DAMUseful thread. Also some thoughts on LightZone.