Leica M9 has a 18.0MP Full frame (36 x 24 mm ) sized CCD sensor . On the other hand, Hasselblad X2D has a 101.8MP Medium format (44 x 33 mm ) sized CMOS sensor .
Hasselblad X2D's sensor provides 83.8MP more than Leica M9's sensor, which gives a significant advantage in real life. You can print your images larger or crop more freely.
On the other hand, please keep in mind that Max sensor resolution is not the only determinant of resolving power. Factors such as the optical elements, low pass filter, pixel size and sensor technology also affects the final resolution of the captured image.
Another difference between these two cameras is that Leica M9's sensor lacks anti-alias (Low-Pass) filter. Removing anti-alias filter increases the sharpness and level of detail but at the same time, it increases the chance of moiré occurring in certain scenes.
Below you can see the M9 and X2D 100c sensor size comparison.
Sensor Size and Resolution Comparison image of Leica M9 and Hasselblad X2D Cameras
As seen above, Hasselblad X2D has a 1.7x Larger sensor area than Leica M9. Larger sensors give photographer more control on the depth of field and blurry background compared to smaller sensor when shot in same focal length and aperture.