Olympus E-P5 has a
16.0MP Four Thirds (17.3 x 13 mm ) sized CMOS sensor . On the other hand, Panasonic L1 has a
7.0MP Four Thirds (17.3 x 13 mm ) sized CMOS sensor .
Olympus E-P5's sensor provides 9MP more than Panasonic L1'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.
Below you can see the E-P5 and L1 sensor size comparison.
Olympus E-P5 and Panasonic L1 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. On the other hand, since Panasonic L1 has 115% larger pixel area (30.47µm2 vs 14.12µm2) compared to Olympus E-P5, it has larger pixel area to collect light hence potential to have less noise in low light / High ISO images.