Where to start...
First take this review with a grain of salt because this place isn't really a hotel, it is a conference center that caters to large groups of military folk and happens to have sleeping quarters. If you are visiting the area for pleasure I would avoid this place like the plague. For a company looking to book an inexpensive conference center you can probably get a lot of bang for your buck here.

1) National: F
For a place that calls itself the NATIONAL Conference Center and caters so heavily to US Military folk I was HIGHLY disturbed that nearly everything in my hotel room was made in a foreign country (mostly China).

2) Rooms: D
The room I stayed in was more similar to jail cells I've seen on prison tours than a hotel room. Cramped, small window, and not comforting. The bed in the room I stayed in faced the door which had a 1/4 inch gap around it that seemed to flood my room with light. With all the room lights turned off it made the door look like something out of a horror movie with an eerie white light all around it.

3) Common areas: F
The furniture throughout the facility was identical to the junk they had in lounges at the college I went to - it looked like it dated back to the 1950's. All the charm of a nuclear fallout facility or a bunker for the apocalypse.

4) Dining: F
To get from certain sleeping areas to the cafeteria (yes, the all you can eat type where you use trays) you have to wander through the unadorned white walled underground labyrinth. In it's defense the halls are very well lit and clean...The food is what you'd expect from a school cafeteria.

5) Grounds/Location: A
The place is on a great piece of land and they haven't messed it up. About 3 miles away (15$ taxi) is an Outlet Store area. About 1 mile away are a few shops and a great little cafe called "Not Your Average Joe's". The hotel has an airport shuttle which runs $20 PER PERSON. A taxi to the airport is only $30 so if you are going with colleagues take the taxi.

6) Conference Center: C
There were 2 conferences going on when I was staying here and they.competed with each other for signage real estate. Not a lot of thought seems to have gone into the governance of where conference signage should be posted, and what is appropriate. One hallway leading to the 2 conferences was littered with signage from both conferences and seemed disorganized and cluttered.

I had read the reviews and I was bracing myself for my stay here.
But I was completely happy staying at the National Conference Center. The rooms are small single rooms but they are absolutely spotless. The bed was confortable. Every staff person I spoke to was unfailingly helpful and gracious. I spoke with the front desk, security, housekeeping and the business office. They were all helpful. The food was delicious and is included in the price of the room. The grounds are manicured. It was a very nice place to have a conference.

In case you have the misfortune of going there, here are a few tips:
1) The rooms are small (because bathrooms used to be shared--one per floor, so when they added bathrooms into each unit, the units became "micro-hotel" style rooms) so do try and get out about, if the weather permits. If you're claustrophobic, it might be a problem.
2) There's about a three inch gap between the bottom of the door and floor, so you'll want to block it with towels in order to shut out excess light and get rest at night.
3) Heating/air conditioning units are quite loud. They bubble and clank constantly (I thought mine was malfunctioning, and had maintenance check it. Nope. They are supposed to be that loud). If you can stand to have the HVAC off at night, you might get rest.
4) The water made myself and many, many of my coworkers ill. I recommend buying bottled water in town when you arrive.
5) The food is very low quality, and not fresh. Several people in my group were nauseated by most of the dishes served, and were reduced to eating salads and picking through a few other items.
Side Note: The cafeteria is only open at certain times, including the beverage cages.
If you want to eat, or drink anything other than tap water, you have to get down to the cafeteria on time. Which means: NO sleeping in on weekends.
6) Cell phone reception is only good in the guestrooms, outdoors, and in the periphery of the buildings. The entire complex is cement, so you won't get reception in most of the meeting rooms or really anywhere inside the buildings. You need to be near a window or outside.
7) There are a few options for doing laundry at this facility. If you use their dry cleaning service, it's VERY expensive. If you want to use the coin laundry rooms, there is one in the north building with 3 washers and 3 driers, and the same thing in the south building. The complex has 2 buildings, housing a total possible capacity of 900 people. 6 washers total, 6 driers...for 900 people. You get where this is headed, right?
8) The free internet provided is plug-in only--no WIFI.
9) There were bugs in my room at times. Many others had the same complaint. Also, I highly recommend checking your mattress for bedbugs upon arrival.
10) Getting away from the facility is difficult and expensive, unless you have (or rent) your own vehicle. The place is isolated on a lot of acreage, and walking to anything becomes a huge task in bad weather. A simple ride to the Dulles Airport from the facility (12 miles) is $20 by NCC shuttle, and $30+ by cab.

In all honesty, the staff members are very friendly. But, if something breaks down, don't expect it to get fixed quickly. And if you want to do ANYTHING (drink a bottle of water provided by the facility, have them hook up a gaming consul in your room, buy toothpaste in the gift shop ), if it's run by/owned/connected to the facility, expect to pay through the nose.

Great place for the business portion of your trip, but the sleeping is horrible. The guest room heating system is outdated as are the windows, so you are either left freezing all night or sleeping in a hot box! There is no in between. Everyone in my group has the same complaints and are miserable each morning due the sleeping arrangements. Perhaps arranging your conference in the fall or spring would be ideal. The facility is great and the meals are fantastic, but it is hard to enjoy knowing that you have to enter your meat freezer room to turn on the heat, which will shortly turn into an oven, which starts another cycle of a sleepless uncomfortable night.