Here's my lowdown on Merion:
It's interesting. It's reeeeally interesting, at least compared the last two snooze courses of Olympic and Congressional. But it comes at a price; the general consensus (not said publicly, but word of mouth and some pointed comments have let the cat out of the bag) that the course is too old, too dated, too short, to defenseless, that the USGA has had to manipulate the hell out of it in order to get it to play tough. There's no graduated rough, they have manipulated many of the fairways to funnel players shots into one spot (force them to hit shorter clubs off the tee or else try to hit a 20-yd wide fairway with the driver), mess with the sight lines and playing angles, put the pins in gimmicky locations, so on and so forth.
Most of the challenge comes from the fact that this course was very much designed to be played with a ball that could be easily curved and shaped. Now it's just not easy to do that with modern equipment. Add in the fact that the course punishes the longer hitters disproportionately, and you can see how people are thinking that it's a gimmicky mess, at least if you're playing in it.
However, from a spectator point of view, this is awesome. Holes 15 thru 18 are awesome (even if 15 and 17 totally suck as golf holes) spectator-wise. Gonna be a great finish tomorrow. The course is still really unique - I haven't ever seen anything like it. Love the quarry hole too!