This passage has always been a stumbling block for me. The idea that it was a mass resuscitation has its merits but that explanation has never quite settled the uneasiness I felt when reading this passage. The whole account has always felt somewhat gratuitous, arbitrary and contrived to me. Especially since the account isn't even mentioned or alluded to by the other Gospels.
However, a couple of years ago, when I was really wrestling with this during a Bible study I sometimes lead, I came across this article which I think explains what was going on here in terms which, to my mind, seem much more reasonable.Matthew 27:52-53 as Apocalyptic Apostrophe: Temporal-Spatial Collapse in the Gospel of Matthew
by Kenneth Waters, from 2003 in the Journal of Biblical Literature.
This particular distribution requires a free registration to read online but a Google search for the downloadable PDF version produces several hits as well.
in short, Dr. Waters argues that this account has all the earmarks of an apocalyptic account and that it was probably inserted to serve as a dramatic flash-forward to the culminating event made possible by the death of Christ - the final resurrection of believers.
It's a 26 page read, but well worth the investment for anyone who finds this passage troubling. I hope this helps someone as much as it has helped me.