I didn't go to antenatal classes, but watched this
They cover this very thing on the dvd. The uber-midwife (so reassuring) says that out of every five women giving birth, one will have an immediate rush of love, three will think: "oh a baby, now where's that tea and toast?" and one will look at the baby and think, "God, what have I done, what an ugly baby..." .
I think this was brilliant advice. I think I fell into the 3/5 category - I had pushed for an hour and a half and was prepped for section, then delivered with a high forceps which meant he didn't cry for well over a minute. I have photos of when I first held him and even then I didn't feel much. I remember crying over him a lot in the hospital, sobbing actually.
For me, the crazy love came some time in the first or second week, helped (I think) by the fact I followed the advice on this dvd and spent the first week at home in bed with him doing lots of skin-to-skin and quite a lot of it with him in a nappy. I also spent a lot of time, as she had suggested, inspecting him. Looking at every last bit of him and also photographing him from every angle so that I came to "know" him on the outside.
I suspect (totally without evidence) that without this it would have taken longer, I don't know why I think that but I do.. there was definitely something about the skin-to-skin and close confinement together that worked well for me.