The games themselves are fucking great, but the ports are utterly horrible - especially in PAL territories. The Orochi Saga port on PS2 and PSP in the UK is bugged to the point of being unplayable in some places.
Apparently the console ports of KOFXIII are damn near flawless, and the PS2 ports of 2000/2001, Maximum Impact and '98 Ultimate Match are absolutely spot on. 2002, 2003 and Neowave had a few graphical errors here and there but absolutely nothing that impacted on the gameplay itself, SVC Chaos and Neo Geo Battle Coliseum were pretty great too despite some lengthy loading times and maybe some graphical inconsistancies. SNK Playmore and Ignition Entertainment haven't done TOO bad of a job for the most part, but their PAL port of The King of Fighters XI has some bugs and glitches that are really, really fucking dreadful in places and should've been ioned out long before retail release.
Such a shame, but it happens sometimes. I remember when they ported KOF'95, Samurai Shodown III and Real Bout to the PSone over here and they were almost arcade perfect with the exception of some long loading times (except SS3 which was nicknamed 'Samurai Slowdown' due to being... well, you get it). I miss the good old days.
Maybe it's time for me to upgrade to an Xbox 360 and get KOFXIII