16MB of textures is not going to be a problem anytime soon, and as far as a few games are concerned, texture compression will save the small 16MB texture RAM on the MX, while the TNT2 will run out of RAM as there is no DXTC support.
Also, although not widely used, the GF2 MX can off-load work from the CPU with T&L (although this is slightly meaningless at the moment as only a few games use this), as well as just being generally faster.