From what I've seen over at Beyond3D, the differences are as follows:
1. Radeon 9700 has an anisotropic implementation that's an improved version of what was done on the Radeon 8500. It still will look worse than the GeForce4 at some angles. To me, this makes it worse.
2. The Radeon 9700 has superior FSAA, for three primary reasons:
(a) More speed, due to higher memory bandwidth and other possible optimizations.
(b) Better sample patterns.
(c) Gamma-correct FSAA.
The benefit of the the higher speed is obvious, and the better sample patterns are almost as obvious for those in the known, but I believe both of those actually pale in comparison to the improvment offered for gamma-correct FSAA. Unfortunately, however, the amount by which the FSAA is gamma adjusted is currently not user-selectable, and will therefore be wrong for many people. Still, it is better than nothing.
A quick explanation of what gamma-correct FSAA does: When the voltage signal is sent to the monitor, doubling the voltage will not double the brightness. That is, it's not a linear response. As it turns out, most monitors have voltage response curves that just happen to fit in well with the human visual subsystem, so that while double the brightness isn't being produced, our eye sees it as that.
What this means is that when doing averages, straight averages are actually not the way to go. It is much better to do a reverse gamma adjust before averaging, and then gamma adjust the output. This won't affect the overall brightness, but will affect averages. While it is true that any average done (texure filtering, blending, etc.) should also do this, it really isn't feasible. But, FSAA can show the problems that result from lack of gamma correctness most when viewing wireframe images. Have you ever viewed an image in wireframe with FSAA enabled and noticed that, from a distance, the lines looked dotted? This should not happen with proper gamma.
In sum: The Radeon 9700 offers better FSAA and similar anisotropic (some say better aniso, I say worse) compared with the GeForce3/4 architecture.