The G2 and Nikon systems are totally different types of cameras - for different photographic purposes. Though the Leica shares the same film format with these systems it is a different type of photographic tool. I use a Leica for street photography in New York City. For me, it is the best system - and the 35 mm ASPH Summicron is my favorite lens. My Nikon attracts too much attention for discrete shooting.
Value is a relative term.
I am no ideologue. Be wary of the deep pocket guys who raise this lens to the heavens just because they own one. With 11-20 years experience in People photography. Make no mistake, the Summicron is a great lens, beating any SLR standard prime into humble submission. I use a Leica and G2 systems and have come to a personal conclusion that there is little difference in the quality of the Leica optics and G series lenses, independent optic tests seem to back this up.