2009 BMW Z4 Roadster. The BMW Z4 is a two-seat convertible aimed at buyers who want an engaging driving experience, bold styling, and luxury appointments. Not as hard-edged as the Porsche Boxster, and not as relaxed as the Mercedes-Benz SLK, the Z4 seeks to bring balanced luxury and performance to the premium roadster market. For more new car reviews, interviews and automotive news visit http://www.kbb.com today.