I played Oakmont two times about ten days before the recent Am. First time my drive, which was hit pretty straight, landed maybe halfway between the center and the left edge of the fairway, and ended up 6" left of the first cut, in very deep wedge-out rough.
The second round I hit the right center of the fairway with a 3 Wd, and then had 9-iron, ending up about 4' left of the green, dead pin high which was in the middle of the green. Hit what I thought was a very good chip, with the ball very slowly trickling as it reached the cup. On a 10 stimp green the ball ends up in tap-in range. Here, the ball rolled about 3' past the cup and then took a dead left turn and rolled off the back. Somehow made the straight uphill 30' for par.
I'd say as difficult a first hole as I'd ever seen. Length not at all an issue unless it's mudball. But with undulating fairways rolling as fast as some courses' greens, it's hard to keep it in the fairways. Very difficult green to hit - - not hard to land it on, but tough to keep it on. Intentionally hitting a downhill short-iron past the cup, even being willing to hit it over the green is just not an easy thing to do. Not so tough an up and in from behind the green, as long as you can control where the balls ends up over the green. But getting it to the right spot over the green requires a good drive and then a very well controlled approach.