I'll second what the other Old Head defenders have said. It isn't perfect, a lot of the routing by dictated by the property but it is a good challenging test with some imaginative holes. Yes, a few seem repetitive and there is room for improvement, though maybe less now if they've changed 10 holes in the past two years -- I saw it in the summer of 2004.
If you are moved at all by spectacular sites, it is worth the price of admission to just to see the place in person, and would be even if the golf course was complete crap. Until they open a golf course at Yosemite National Park, I think Old Head will remain the leader in the clubhouse for most spectacular site (though I admit I haven't seen Doak's work over there on the bottom of the world, just pictures, and those obviously aren't the same as being there) But don't let that fool you, the golf course is still first rate, it would be worth playing even if it was saddled with Carnoustie's setting.
I think Tralee is underrated as well. There are a few holes you could miss on the front nine I suppose, but the back nine is world class. Matt Ward's right about Old Ballybunion, other than the 2nd, until you pass its lackluster par 5 4th and 5th you might wonder what all the hubbub is about. But the 6th through 18th comprise bar none the finest 13 hole stretch in the world. Not letup, no weak holes, just one amazing hole after another.
One parting thought. If you miss Old Head, you miss what is IMHO the most intimidating tee shot I've ever seen, on the 12th. Imagine standing on the edge of a cliff several hundred feet above the sea, with howling wind, facing a tee shot that cuts over the chasm, aiming at a cliff face on the other side, at a blind angled fairway that sits above the level the tee is on. PB's 18th is a wide open muni by comparison. The only thing that would make it tougher would be to have seabirds dive bombing you while you take your stance. I don't think they'd have the guts to design a hole with that tee shot if we still played with balata and persimmon.