It offers a spectacular view of DC and the living history exhibits in the summer add to the over all interest. Over the last 6 years I've been visiting periodically they have been slowly renovating Arlington House and the finished rooms are very nicely done.
The downside is that at any given time, about half the house has been closed and that remains true today.
The slave quarters have been renovated as well and while some of it is very nicely done, if you are observant you'll notice things like Ikea style bed frames using modern fasteners. That spoils the experience in my opinion as seeing original fasteners is an important part of the experience.
Also, there is no indication of the location of the summer kitchen, or any description of the original purpose of the "museum" building.
Finally, the current tour does not discuss the faux marble pillars or facing on the building, which is an otherwise very interesting insight into the architecture of the time.