Invest in earplugs!
While this apartment is very nice and fairly clean on the inside, the surrounding area is what may give you some trouble. As other guests have said, homelessness is prevalent in this area. However, they are only human just like us so it wasn't an issue for me. They didn't bother me anytime I was out and I walked an awful lot.
However, this unit is definitely in a busier neighborhood. There is constant noise...from the people on the street to garbage trucks to motorcycle and truck engines revving to music blasting to emergency vehicle sirens...all day. every day. If you are a light sleeper, it will be a huge adjustment and I would highly recommend earplugs for the evening hours (it's the only way I was able to get any sleep.)
One of the good things about the area is you are VERY close to Union Square and the shopping districts..only a couple of blocks up the street.