Not the most glamorous-sounding route, but I took it rather than take the motorway back to Dublin and was pleasantly surprised by this road. Good visibility, nice bends, and mostly good surfaces. Smiley face all the way!
The main downside is hitting a few villages and their 50km limit, but otherwise highly enjoyable. Of course, the usual caveat regarding Irish roads in intensive agriculture areas applies. Farmers have full licence to spread as much shite as they want on the carefully-engineered surfaces, and seem to do so with great zeal. It's a bit like animals marking their territory. At this stage, the whole country smells of shite - but that's another story. Watch out for it in the wet - lethal.
I ended this route at Athy because the town is a traffic nightmare, even on a bike. Almost met my maker when an octogenarian deliberately pulled out in front of me without a care in the world and with his caravan behind him.
After Athy, the road is almost straight and has a bizarre 60km limit most of the way to Naas, so do anything you can to avoid it. Motorway would be better.
So, an unexpected bonus in the not-so-boring Irish midlands.