One of the most exciting aspects of MMA is the sheer variety of fighting styles you'll see in a single event. The original's repertoire was rather extensive: boxing, kickboxing, muay thai, judo, Brazilian jujitsu, and freestyle wrestling. UFC Undisputed 2010 adds three more fighting techniques into the mix: sambo, karate and Greco-Roman wrestling.
This developer video goes into more detail about the three new styles added to the game, emphasizing the differences between karate and muay thai, for example. With the ability to "combo anything together" in 2010, the added move list should provide a number of interesting and painful combinations to explore.