I owned a 5900XT for several years and it was a reliable performer for most of my old games, and could gasp and struggle through new ones tolerably well for a few years. The OpenGL support was also consistently good. but came at a heavy performance hit, and was removed from the GeForce 6 and 7 series. The GeforceFX's were really quite nice for DirectX 8 games, and the angle-independent anisotropic filtering wasn't matched again until the Radeon x1*00 cards came out.
Didn't everyone (sane) skip them and go to the 6000 series when available? I thought the 5000 series from nVidia was absolute trash.