The park was excellent.  We had our own issues on this trip, but with the trip on the Metro being ~30 minutes to DC to see the sights you can't beat it.  The spot we had was definitely beautifully level right-to-left.

It's a little strange to be in the middle of a suburban area and suddenly in a gigantic green space.

The only issues I really had were:

1. The bathhouse situation.  I don't know if it was due to the scout troop that we had to share the bathhouse with or not, but the showers were always filthy, even when they were supposed to have been closed for cleaning.
2. The Balt-Wash parkway kind cuts through the Greenbelt Park and it can be very noisy, which is a bummer when you have to keep your windows open.