After reading his essay, I only felt two of his arguments were convincing. The first one is that bereavement experiences tend to occur weeks after the persons death, not within days. The second argument is that 40% of bereavement experiences last for several years. To the first argument, I can only point out that, although many don't start this early, some do, such as Allison's own case (as recounted in Resurrecting Jesus). Furthermore, positing that the disciples had bereavement visions a few weeks (perhaps two) after the crucifixion just doesn't seem like a big stretch to me. For all we know, they could've have pushed the appearances back a little to make it seem more convincing.
The latter criticism of the two is a hard one to solve. I think, as Allison does, that a good explanation may be the fact that there was some expectation. Jesus declared that he would be resurrected. So, the disciples would have classified certain visions as resurrection appearances, and other ones as mere visions. O'Collins foresees this objection, but responds to it by appealing to the lack of Jesus visions in later material, such as the book of acts. Sorry, but I just don't feel like this criticism is particularly good. There may have been many postmortem visions of Jesus that simply were never recorded. I know it's an argument from silence, but it's still a strong possibility. Another possibility is that, as many scholars have suggested, the visions ending after "forty days", is allegorical, and really means "a long time".
I just want to conclude by saying that, although studying bereavement experiences in the modern world can be very useful, I am skeptical of how far they can really take us in terms of understanding the Resurrection. In the cases documented by Dewi Rees, only widows and widowers were interviewed. The disciples, as O'Collins rightly points out, are very different than widows and widowers. The disciples had not only a lot of grief, but a lot of messianic expectations and possibly even an empty tomb to account for. Furthermore, they lived in a different time with a different mindset. For example, Rees' study showed that the bereaved rarely ever talk about their experiences. However, in ancient times, these sorts of experiences were well understood; as a matter of fact, the gospel writers went thru great pains to emphasize that Jesus was not one!
So, despite himself, O'Collins is right- just for the wrong reason. We have no precedent for what the disciples went thru, so we shouldn't be surprised if their testimony seems a little bit different than what we see in these kinds of modern surveys. And as a final note, O'Collins reassured me that his criticism of Bereavement experiences was so far the only one done by a professional scholar. So, if you want a copy of O'Collins essay, just send me an email.
O'Collins didn't send me his essay from the Irish Theological quarterly, but his arguments from the appendex of his new book, Believing in the Resurrection: The Meaning and Promise of the Risen Jesus. Nonetheless, the document still contains all the arguments from his earlier essay, as well as some new ones.