Both Samsung NX2000 and Samsung NX3000 have 20.0 MP resolution sensors but Samsung NX2000's sensor is APS-C (23.5 x 15.7 mm ) and Samsung NX3000's sensor is APS-C (23.5 x 15.7 mm ).
Since Samsung NX3000's has a larger sensor area with the same resolution, this means that it also has a larger pixel area hence better light collecting capacity for a given aperture compared to Samsung NX2000.
Below you can see the NX2000 and NX3000 sensor size comparison.
Samsung NX2000 and Samsung NX3000 have the same sensor sizes so they will provide same level of control over the depth of field when used with same focal length and aperture.