Sani's sprites are made with no anti-aliasing and half the resolution (that is, each "pixel" is actually a 2x2 block of pixels, much like the character sprites).
You can see the difference here:


So they don't have as much detail, but they're a little more truer to "pixel art" and a little more consistent with the actual gg2 sprites. Whether that's a good thing overall, eh. I prefer the originals, but that's just me.