KOF XII/XIII sprites were rotoscoped from 3D models. They did this because pixel art is far more expensive. For reference, SNK stated that it costed them around $1m per 3D character in KOF XIII. But the savings come with tweaking the models when they rebalance moves. They can just alter the model. 2D sprites have to be redrawn.
SNK Playmore published a great article which I cannot seem to find now with details on their technique.
The reason purists don't like the look of the game though is because SNK was traditionally known for superb pixel art.
http://www.noe-v.com/images/articles/terry_sprites01.jpg
KOF XII/XIII sprites were rotoscoped from 3D models. They did this because pixel art is far more expensive. For reference, SNK stated that it costed them around $1m per 3D character in KOF XIII. But the savings come with tweaking the models when they rebalance moves. They can just alter the model. 2D sprites have to be redrawn.
SNK Playmore published a great article which I cannot seem to find now with details on their technique.
The reason purists don't like the look of the game though is because SNK was traditionally known for superb pixel art.
http://images.wikia.com/snk/images/e/e8/Kof99park3bglite.gif