Chess 1 was a hit, no doubt about it. Chess 2 seeks to build on the greatness of the original while addressing a few problems and also going in a new direction. There are now SIX ARMIES to choose from, rather than just 1, creating 21 matchups instead of just 1. There's a new win condition for crossing the midline of the board with your king (in addition to your grandpa's checkmates). There's also a bidding mechanic called dueling that makes memorized openings even more impractical, and emphasizes adaptation and reading the opponent's tendencies.
The Six Armies:
Classic (balanced)
Nemesis (favors pawns)
Empowered (favors knights/bishops/rooks)
Reaper (favors queen)
Two Kings (has two kings!)
Animal (wild card)