Short answers, pulled from the story.
Street Fighter EX2 was co-produced by Capcom and Arika and originally released as an arcade game for the Sony ZN-2 hardware. It was the second spin-off of the Street Fighter series and the direct sequel to Street Fighter EX.
Excel Combos, with "excel" short for "extra cancel," let players chain basic and special moves together within a limited time window. A player starts with a basic move and can follow it with a different basic move or a special move, but no move can connect directly into the same move that preceded it.
Street Fighter EX2 Plus arrived in arcades on the 11th of June 1999. It introduced Meteor Combos requiring all three stocks of the Super Combo gauge, added new characters including Sagat, Vulcano Rosso, and Area, and revised the Excel Combo system to permit connecting the same move twice in sequence.
Street Fighter EX2 introduced Blanka and Vega from Street Fighter II to the EX series for the first time. New original characters Sharon, a redheaded female special agent, and Hayate, a Japanese swordsman, also made their first appearances. The hidden roster added Shadow Geist and Nanase, the latter identified as the sister of both Hokuto and Kairi.
Takayuki Aihara, Shinji Hosoe, and Ayako Saso, all former Namco composers, wrote the Street Fighter EX2 score. Scitron released a soundtrack CD on the 18th of June 1998. A 13-track arranged album followed on the 23rd of July 1998 through Suleputer, featuring additional contributions from Yasunori Mitsuda and Toshimichi Isoe.
PSX Extreme called Street Fighter EX2 Plus "one of the most enhanced and entertaining Street Fighters ever" and described it as "one of the most polished looking fighting games to date" in comparison to SNK's Fatal Fury: Wild Ambition. GameSpot praised the new characters and graphics but noted static ending sequences and a perceived lack of originality.