If the US Open was played free of spectators, I could not imagine a better test of golf than Merion. It forces players to hit all different types of shots. The long par fours still remain long, especially at holes 5, 14, and 18. The greens are the real test at Merion, meaning the golf course will always stand up to technology.
However, it seems Merion is a very tight fit for a big tournament. The course held up okay against the onslaught of galleries in the Walker Cup. Yet we should remember that the Walker Cup allows for much more flexible gallery movement. The course was only roped off around the greens, and there were only a few groups on the course each day. This situation meant that we could wander the fairways comfortably without any sense of claustrophobia. This will not be the case at the US Open, where all playing areas will be roped off, meaning a very cramped affair for galleries of US Open size. Furthermore, problems areas during the Walker Cup, such as between 3 and 6, will only be more pronounced with more people.
The golf course itself is not out of date. A golf course does not need to be a death march of long par fours to be a US Open test. However, the size of property at Merion is a great cause for concern.