Stumbled across a perfect condition used copy of KOF12 for just 100Y today... yes that's about all it's worth after 13... but it's still nice to have it back in my collection, this time for PS3 after i gave my 360 away after moving to Japan.
Anyway, playing both of those recently, of course they have the fantastic sprite work, and look great overall... but there are some things that hold them back, and 14 does better i think. Some characters being uncharacteristically bulky, and there being too much animation in the backgrounds have been noted before. But, my personal pet peeve is the use of color. They got the backgrounds looking plenty nice, but the default character colors are a combination of desaturated clothes and burnt skin.
You can fix a few using the colour edit but it's not always perfect. And on some stages (worse in 12) there are huge shadows that dull the characters even more and make them blend into the background too much, and lighting that alters the character colors further with glows.
I'm glad 14 has the typical bright colors back, so the characters are easily distinguishable from the backgrounds. None of this stage shadows and glow garbage, and the stages themselves have an amount of animation much closer to the original games. I haven't counted, but i think we've already seen more stages than 13 had too - lack of stages would be really apparent with a roster this big. Overall i think there are more good ones than 13, which has a few really plain looking backgrounds.
Playing 12, i do like seeing those sprites at full size, pixels and all... allows you to catch more of the detail. But, the game was definitely played better with zoomed out characters in 13 (this isn't AoF!), so i'm glad that was retained in 14 too.