what is the story with brooklyn landlords constantly knocking on the door and dropping in for no reason as if you aren't paying them rent for the space.  i have never experienced these interruptions in any other city. 

If you are a subsidized tenant, meaning your rent is paid in full/part by a governemental agency, the landlords have a duty to the city regulators to "maintain" the apartment. Which means constant check ups/visits to your apartment.

If not, then your landlord is violating your tenants rights, and you need to file a formal protest with the local courts.

Actually, the TRUTH is that if you receive a Section 8 subsidy, you have one (1) annual inspection by a Section 8 representative. It's a two-way street; it's an opportunity for Section 8 and the landlord to make sure the tenant is keeping the apartment properly maintained and not destroying the property or hoarding, etc. It's ALSO an opportunity for the tenant to let Section 8 know whether the landlord is also maintaining the property properly, instead of letting violations of the Warrant of Habitability pile up without making necessary repairs.

"Constant" check ups/visits can be harassment on the part of the landlord because it can be seen as a violation of the tenant's right to quiet enjoyment of the apartment they have a lease for (the lease is a contract) and pay rent for. 

If the tenant fails the inspection, they can request another appointment for an inspection and make a serious effort to cure the problems. The landlord can do the same. The subsidy doesn't get yanked automatically just because you don't pass the first time.