Boston City Hall is the perfect candidate for an eco-brutalist makeover. Add the SF Hyatt Regency while you're at it.
Europe's eco-brutalist buildings are gorgeous. [1] [2]
Boston City Hall's problem is the windy open plaza. The building stands as the only imposing mass in that area. If there were trees and other shelter, one could admire it. But as it stands today, it intimidates.
All that being said, positives changes are happening. Cop slide is definitely one of Boston's must see attractions.
Partly, it's definitely the combination of the building and the plaza. I don't know the history but it seems as if commerce (cafes and the like) haven't been especially welcome on the plaza though they'd admittedly only be attractive for 4-5 months out of the year.