I very recently completed a stay at the RC Pentagon City.

I booked two rooms over the 4th of July weekend (July 3rd-7th) that were upgraded to the club level using RC card upgrade certs (which was an adventure in and of itself). As usual, the concierge reached out prior to our stay and asked if there were any particular requests. I asked for a room with a view of the fireworks, and if that wasn't possible, a room on a high floor or a room close to the club lounge.

Upon check-in, I was greeted as a Titanium and given a choice of welcome amenity (some chocolates or champagne/wine) or points. I opted for the points, since I could get the food and booze at the lounge. I did ask about upgrades, and were told that they would have been happy to upgrade us to a suite, but no suites were available. This jived with the availability posted online, so no issues there.

We ended up getting two rooms on the 18th floor that ended up having an AMAZING view of the fireworks.

The lounge was very enjoyable.
Breakfast was nearly the same every day. Eggs, bacon, oatmeal, chicken sausage, lox, and assorted breads/spreads/cereals.
Lunch was two different types of sandwiches (one vegetarian, one meat), along with a soup, and assorted sides.
The snack presentation was the weakest, they took the chips and crackers from lunch and put them out in addition to some pickled vegetables.
Evening hors d'oeuvres consisted of 2-3 hot dishes, with assorted sides. I particularly liked the filet mignon when it was available. My wife took a strong liking to the crab claws.
Desserts were varied and delicious.

The fitness center is well-equipped, though I don't remember if they have free weights or not. There are plenty of machines though. The pool and steam rooms were closed during our stay, but the sauna was still available.
They do NOT have an on-site spa, but they do offer spa services in your room or in a massage room located in the locker rooms of the fitness center.

As far as location, I thought the location was pretty good for tourists. There is a lot to do in the vicinity, including visiting the Pentagon, the Pentagon Memorial, Air Force Memorial, and Arlington National Cemetery. Pretty much directly across the river in DC proper, you will find the main DC tourist attractions, including the presidential memorials, the Washington Monument, Mall, Reflecting Pool, and Smithsonians.

The RC itself is attached to a decently sized mall with a nice food court and several restaurants are close by (I'm partial to Matchbox, myself). The mall also has a direct tunnel to the DC metro (Pentagon City Station), and it is ~10 minutes away from Washington National Airport (DCA).

For those that care, there is a Costco in the shopping center across the street from the mall. This particular Costco has beer/wine available (no liquor).

We requested and were given 4pm check-out.

Oh, one last thing. We ended up parking our two vehicles in the mall parking garage. It is $18/day. Something else to note is that one of the drivers lost their parking ticket, and had to go to the booth to say they lost their ticket. They were charged $18 (the daily maximum). So just throwing that out there.

Happy to answer any additional questions as well.