IQ wise it's pretty good to excellent, the only real thing it's criticized for is the painfully slow focussing. It's not an AFS lens (internal focus motor), but rather screwdriver drive, and it must have a really high geared focus cam, as it takes a long time to scroll from near to infinity focus, IIRC, it's one of Nikon's slowest ever focussing lenses.
When I had it some years ago, I negated this as much as possible by using the focus limiter to prevent the lens hunting over it's full range, and it then worked quite well. Not a lens I was would use for fast moving action, but on the higher end bodies with the more powerful focus motors, very usable. It has VR but it's first generation so realistically only good for about 2 stops, rather than the more modern set-ups of 3-4 stops.
Overall, it's not a bad lens optically you just need to be aware of it's limitations. Having said that, I do find that my 70-200 F2.8 VR II combined with the TC20 E III, gives very similar results, with much better focussing and VR. The one really good thing about the 80-400 is it's size. It's a really compact lens for a 400mm and that might well be a consideration ?