I wore Keen (Arrows I think) trail sandals, with socks. Great ventilation, good support, thick shock absorbing sole, comfortable. The sturdy toe-guard provided great protection on rocky downhills. Only when the rain was really heavy did my feet get soaked and without any noticeable negative effects regarding blisters. Only minor irritant was that about every two or three hours a small pebble kicked up from the trail got into the sandal through the sandals's leather upper open fretwork. I just regarded it as the Camino "talking to me" saying it was time to stop and take a 2 minute break, drink some water and get rid of the pebble.
Thoroughly recommend Keens. I really felt they were ideal for the Camino and was glad I left my Meindl mountain boots behind. The weight reduction with every step, on every km, for all 800km's being the main benefit. In Aug/Sept I encountered 5 or 6 rainy days but most days were bright and sunny, and got swelteringly hot as the day progressed onwards, would not like to have been in boots. I was reminded of my Meindls by some graffitti on an underpass along the Camino (a drawing of a pair of boots with fire coming out the top and a thermometer registering 60C sticking out of the sole) titled Botas de Fuego.
Even if you got wet walking in the Keens (say it was raining for an hour or two in the morning), I found that if you stopped for coffee, left the Keens in the sun or wind to dry, changed into a dry pair of socks that by the time you were ready to start walking again the Keens were dry.
Its always going to be a trade-off whatever footwear that you use on the Camino, but the Keen's worked for me, and were well able to deal with the spots of the Camino where there is difficult harsh terrain. Considering most of the Camino is on waymarked paths and not difficult, harsh terrain they are a good compromise. Would I wear my Keens climbing Carrauntouhill (Irelands highest mountain)? Definitely not, thats Meindl territory.