The Leica M-E has a CCD sensor type which is better than most cameras that are a comparable age to it. Most cameras of a comparable age and type to it have a MOS sensor type. 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 amongst all comparable spec digital cameras that have been on the market for a similar time to the M-E.
A MOS sensor type is the worst sensor type amongst comparable types of camera.