I live in DC and have been lucky enough to play both courses at Congressional many times over the years--including the Gold course several times while the Blue course has been under construction. I haven't walked the renovated Blue, but a number of holes are very visible from the clubhouse and Gold course. A few random thoughts:
1. The changes have substantially eliminated the mounding around many of the greens (and some fairways). To my eye, the holes look better and will be more interesting, but the expectation is also that conditions will substantially improve, since moisture won't be channeled toward the greens and fairways. I think they're also hoping that tree removal will improve conditions as well.
2. There are now many more cross-property views, which are quite stunning.
3. It's my understanding that the PGA of America has been very involved in the work, given the future events they've agreed to hold there.
4. Until these changes, my favorite nine holes on the property were the 9 holes of the Gold course (1-5, 15-18) on the same side of Persimmon Tree Road as the clubhouse and Blue course. Or at least 8 of them--I find 18 Gold to be out of character. Look forward to seeing if that changes, but from a distance, it looks like Blue will be very very good.