Go with AC when choosing character for best results.
The Gamecube version of Capcom Vs SNK 2 EO plays exactly like its PS2/XBox/Dreamcast counterparts. The only real difference is you're given the option of "AC-ism" or "GC-ism" after selecting your character(s). GC-ism relocates all the special attacks to the C-Stick (right analog stick). GC-ism will immediately irritate Capcom fighting fans. AC-ism plays exactly like your typical Street Fighter game. Thus, it's prefered.
The graphics are Old School 2-D. And this is good, considering that Capcom fighting game fans expect as much. The clasic handdrawn look really captures the feel of the genre. Very colorful, cartoon/Anime-esqeu.
The usual fireballs, spinning kicks, "SHORYUKENS"... are all here in there native half-circle/quarter-circle, punch/kick form. And the machenics hold up quite well despite their age. Personally, I enjoyed this game quite a bit.
The character roster is a diverse mix of Capcom and SNK brawlers. From Street Fighter to Dark Stalkers to King of Fighters to Fatal Fury... Old School favs are pretty much covered. The only thing I found missing were some of my favs from Marvel Vs Capcom's "Capcom" line-up: Mega Man, Jill Valentine, Captain Commando, Jin, etc... I love those guys. Where the Hell are they? Come on, Capcom...
All in all, Capcom Vs SNK is a much needed excellent 2-D fighter for the Gamecube. Just don't let anal reviewers discourage you from it.