I've been to Galicia in 2000 and 2002 - started in Ribadeo and followed pretty much the coastline. Even though they are deadend roads the stunning scenery at Punta da Estaca de Bares and Cabo Ortegal are worth a detour. El Ferrol can be bypassed IMO.
La Coruña might put you off, as it is quite a big city, but I liked it a lot - built on a peninsula you have the sea on both sides: one with an endless beach and the Domus museum (Casa del hombre), the other with port, castillo and beautiful old town.
Headed then to Santiago de Compostela straight away - must see in terms of architecture, atmosphere, people and wide range of accommodation and restaurants (try tarta de Santiago...
). However, that way I missed the Costa de la Muerte - a big mistake according to my Spanish teacher...
Cabo Fisterra should not be missed, be careful with service stations though (I had to ride quite a while at low revs until I found some fuel at the end of the world).
Further south along the coast (C-550) you should stop at Castro de Baroña and stroll through the foundations of an old Celtic village - very impressive.
Approaching Padrón try the famous Pimientos de Padrón - small green peppers only growing in this region, fried and sprinkled with coarse sea salt and just delicious). I can also recommend the traditional dish Pulpo á feira - boiled octopus tossed in oil and paprika.
The coast is still beautiful and offers great beaches and even the occasional pista (unless they have been all paved in the meantime...) but is very time consuming. So you can always cut short using the main roads if you run out of time. Pontevedra is worth a visit, Vigo is not so pretty.
I went to Baiona (fortaleza and playa) and carried on to A Guarda, the guardian at the border to Portugal. Great place: wonderful views from Monte Santa Tecla (with the additional benefit of the remains of another Celtic village), picturesque harbour and one of the best campsites of the whole journey.
If you want you can nip into Portugal at Tui (cathedral!) by using the old bridge that was built by Gustave Eiffel. I followed the river Miño northwards for a while and then went back into Galicia. The small town of Ribadavia has one of the oldest and best preserved/restored Jewish quarters in Europe.
After Ourense I decided to follow the river Sil upstream to see the breathtaking canyons (viewpoint Os Balcones de Madrid at Parada do Sil and nice campsite nearby) and just enjoy the meandering roads in this area.
One last highlight are As Ermidas - just leave the C-536 at A Pobra de Trives and head towards Manzaneda and then further east. Incredible tiny twisty roads that ultimately lead you to an impressive church in the middle of nowhere (As Ermidas). Shortly before you join the C-533 again you should stop and look back into the valley (how would I have loved to post some pictures here but I only took slides at the time...).
If you need further details just drop me a pm.
Have a great trip!
Ela