I know I might be hitting a touchy subject, but I'm prefacing it with this so I can clarify right away: I don't want a Psak, or who holds what. That's for each person to figure out... I just want to know what all the issues are with respect to the Boro Park eiruv, and why someone would hold what he does.
The second link, which itself contains many relevant and detailed links, addresses the technical issues of the geography, demographics, and (artificial) geology of Brooklyn that govern the permissibility/restrictions of an eruv. The first link addresses a non-legal complication in the case regarding the authenticity of influential documents.