It is a little bulkier and not as sleek looking as the Akai MPC500, which falls into the same category of course.
The roland site gives this detail:
The newest member of the SP-sampler family breaks ground with innovative features such as Loop Capture, and Super Filter. The SP-555 is fast and powerful, but one thing has been preserved from previous SP models: fun! It’s the ultimate toolkit for DJs, producers, sample-based musicians, or performers who want to take their act to the next level.
– Ultra-easy sampling with innovative Loop Capture feature
– Versatile sampling through Line input, phantom-powered Mic input,USB audio streaming, and WAV/AIFF import
– Dozens of killer performance effects, including Super Filter and DJFX Looper
– Audio interface capability with any DAW or DJ audio application (Cakewalk SONAR LE included)
– Large Sample Memory via CompactFlash (up to 2GB)
– Bundled Wave Converter software (Mac and PC) for importing and exporting WAV/AIFF files
– Infrared D BEAM controller and V-LINK compatibility for high-impact performance