The Leica M-E has a CCD sensor type which is better than the MOS sensor type found on most comparable spec cameras that are a similar age to it. 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 cameras of this age and spec.
The worst sensor type amongst comparable types of digital camera is MOS.