The Leica M-E has a CCD sensor type which is better than the MOS sensor type found on most cameras of this spec and age. CCD sensors produce high quality, low-noise images but consume a lot more power than CMOS sensors. CCD is the most common image sensor type used in digital cameras.
A CCD sensor type is in fact the best sensor type across all digital cameras that have been available for a comparable time to the M-E.
A MOS sensor type is the worst sensor type across comparable types of digital camera.