From what I saw firsthand at E3, it looks like they're doing them right. Everyone was playing the SF2 ports to death on the demo kiosks (once in a blue moon, someone would be playing Legendary Wings or Forgotten Worlds instead), so I got a good amount of time to play and watch them. Audio, animations, sprite size, fonts, and framerate seemed accurate--from what I could remember anyway. The AI was DEFINITELY based on the original arcade games, because I was whupping the CPU's butt taking advantage of the usual patterns exhibited by the characters (Jump up, roundhouse to Zangief; low kicks to Balrog; Hurricane kicks to Chun Li and Vega; etc.).
Controls were okay... I dunno... don't like the Xbox pad for fighters...
Wish they had online play, but oh well--it'll be nice to finally have true arcade quality ports of these games at home that don't sacrifice animation or something else.