Expensive but it's a great apartment building. You get a lot of space, there's a deli run by a nice Korean family, and a seamstress/dry cleaner, and a barbershop. There is no gym and there is a communal laundry room. which are downsides.

Great overall apartment experience.

Might be a bit far for some, but there are two nearby bus lines heading downtown, and shops/restaurants nearby on Wisconsin Ave. For the outdoorsy type, the Glover Archibold trail is adjacent to the building, and for the cyclist it's an 8 minute ride out of DC on MacArthur Ave into MD.

4000 Mass is a great location for wanting to live in a quieter neighborhood, but also being close to the city. Close to American University for students. Parking is expensive if you choose to park in the garage, but plenty of street parking.

The floor plans are spacious. The property is secure and the community is welcoming (families, young professionals, some elderly, international mix). The leasing office is very accessible and usually responsive.
This is a full service apt bldg which hosts a breakfast cafe/lunch counter, small 7/11 type market, full service dry cleaner w/ wash-n-fold options, front dest clerk/package valet/bellhop. Bike rooms, extra storage and luggage storage are all available and included with the lease. Parking is an add on. So if you don't need it, you don't pay for it (they have 7 garages and outside parking).
I will say, noise travels easily and rugs are mandatory but bare feet or shoes on hardwood is what it is. There are 3 or 4 bus stops just outside, so the commute is quite convenient to all of DC. The new Giant on Macomb is near many restaurants, banking and boutiques; they are walkable. There's a farmers market at the corner during the warmer months--so fresh local produce is a nice bonus. Most people walk Nebraska Ave. to get to Tenleytown. There's no gym…but honestly--you'll be outside enjoying the grounds and the neighborhood/or you can just have your own equipment 'cuz you'll have the space. The National Cathedral is just our the window and also walkable!!
The bad thing about this place: only one set of elevators--so if you live at the end--you have to walk--but the leasing office is cognizant of this and they were able to give me us a parking spot next to the stairwell nearest our unit. Also there are several secure entrances, therefore the elevators aren't mandatory.
Overall--great place to live.

Pros: Value, size, view, distribution.
Cons: The walls are thin and the location is a bit far from bars and restaurants
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If you are looking for a quiet place, then these apartments are great. Definitely very family friendly and the units are spacious.