I love these, I have several pairs of Birkenstocks and bought these to ruin on holiday as they were cheaper than my other ones (Yara) and I was going to be doing some miles through souks and sand-dunes. As it turned out, they looked so fab with my about town clothes that they stayed in the UK and have been my sandals of choice all summer (my Yara's have hardly seen the light of day!) Many people suggest going a size down and I have found this with the Birkenstock fit, but I read someones review about the fit on here and they suggested that if you find the size you normally wear and choose a narrow fit, I did this and found that they allow for foot movement without catching your toes on the rim (important with this style as there is no toe post to keep your foot anchored back onto the foot-bed and the ankle strap on any Birkenstock shouldn't be fastened tightly).
Most Birkenstocks need a couple of miles to wear in the foot-bed, if you find them initially uncomfortable persevere its worth it.
THESE WOULD HAVE GOT 5* but one of my sandals must have had dodgy adhesive to stick it together as they started to come apart after the third outing - I stuck it back together myself (no dramas) but its a shame as I haven't had problems with any other of my 5 pairs of Birkenstock s.