Breaking a lease agreement

IF the landlord fails to take effective action--which could include evicting the other tenant for "disorderly conduct," or conduct which disturb his neighbors--after written notice and a reasonable opportunity to act, you *may* be able to break your lease without having to pay future rent (see below). The reason I write "may" is that you will be alleging that the landlord is allowing a condition under its control (another tenant's disturbing conduct) to persist which violates either or both of the implied warranty of habitability (effectively  makes your unit not reasonably habitable) and/or covenant of quiet enjoyment (ability to use your rental unit free from unreasonable disturbance).
However, these are subjective standards: there is no hard-and-fast, quantitative way to tell if these rights were violated (i.e. it's not straightforward, like failing to pay rent). If the landlord were to sue you for breaking your lease, for the as-yet unpaid rent, the matter will go to a judge who will evaluate if the condition were bad enough as to warrant breaking your lease. Some judges (particularly nonsmokers) could agree with you, that this was not a condition you should live with; other judges (particularly smokers) might disagree and feel it was a minor annoyance or common incidence of apartment living and did not legally justify breaking your lease, and therefore hold you to the lease--you'd have to pay the rest of the rent due under the lease. You have to be willing to accept the risk of being found liable for the rent if you do this; you can't guaranty that you will be allowed to break the lease without penalty.
IF you are found to have validly broken the lease, you should get your deposit back (and could sue the landlord, such as in small claims court, if you don't). But you will not get your rent for the time you have lived there back: you did in fact live there and have to pay for having done so. In court--if the landlord sues you or you sue him--you *may* be able to convince a court to give you a part of it back, for the impaired conditions; however, in 7 years I have been doing landlord-tenant law in NJ, I have *never* seen a tenant get all their rent back--and generally, no more than 20-30% for even worse conditions, like lack of heat, extensive leaks and black mold, etc.