On my first international trip many years before there was such a thing as Unesco World Heritage sites, I bicycled up to this area from Dublin and stayed atvavyouth hostel across the road from the Monasterboice site. It was a lovely site and the monasteries, dedicated to group work, prayer and scholarship far from the remnants of "civilization" were quite well preserved and signed, right down to the sink (lavabo, Latin fans) in the kitchen.
As the rational notes, this group focus differs from those of the other early Christian monastic sites.
I also visited the Kells and Glendalough sites in spots that truly earn Ireland the name of the Emerald Island. As many scholars ackowledge the Celtic contributions to the preservation of knowledge during a very confused time in the post Roman Empire, this is certainly worthy of inclusion