When UFC 3 was released, EA invented this 'loco-motion' combo combat system. Since then, the game has been declining.
UFC 5 is merely a slight upgrade to an already broken video game series.
Until they return to the drawing board and create an MMA game that doesn't feel constrained by an arcade-style combo button fest like Undisputed 3. As time passes, I believe they will continue to fail and lose even more players.