1 hour slots are convenient. Delivery is rarely late. Substitutions are very infrequent. The 2 main improvements I'd like to see are:
1) more careful and thoughtful packing of bags e.g. not packing sliced bread underneath potatoes (this is my main criticism of Ocado's service); and
2) a better SatNav system that would enable customer locations to be added for future deliveries (I live in a rural area & Ocado's SatNav consistently sends the driver to a neighbouring property accessed from another road).