This is how an expansion should be: Fight! Round 2 is full of new options, rule subsystems and move elements to emulate just about any fighting game, though the main focus seems to be games like Samurai Shodown and Soul Calibour (more complex weapon and armor rules), Guilty Gear and BlazBlue (all kinds of exotic special moves and risky instant kill attacks), Mortal Kombat (various kinds of finishers) as well as some King of Fighters games and the "vs Capcom" series (helpers and tag team super moves).
There are also rules for mor unorthodox "fighting" games, from social combat to traditional fantasy to DBZ-style battles where everyone can fly (turning the simple, one-dimensional battlefield into a two-dimensional grid). Even a Tokusatsu and/or mecha campaign is handled.
I can't recommend this enough if you already liked the core book. If there's something you couldn't properly emulate with Fight!, it's very likely you can do now with Round 2.