I've got a good spread of Canon L primes; 14/2.8, 35/1.4, 50/1.2, 85/1.2, 135/2 and 300/2.8 (I plan to probably get the new 24/1.4 - if not, the old). They're all very good lenses optically, some better than others (the 135 and 300 are very sweet, the former a bargain amongst Ls). The 85 is a portrait lens like no other. But the 50 is very impressive. Somewhat controversial (akin to the Zeiss 1,5/50 Sonnar) due to the "focus shift issue." But in real world shooting and with a bit of knowledge - not an issue at all.
It's a shame one can't compare L glass to M glass directly, digitally; I think the AA filters on Canon bodies really hurts potential sharpness. I look at files from the M8 as compared to the 1D2N and L glass and there's no comparison. Some day maybe I'll try a comparison on film. Gear tests beyond the "hey, it works" kind aren't really my thing though...