So I'll preface this by saying the following:
1.) I would have never read this of my own accord. I read it only for book club.
2.) I was skeptical going in.
3.) Though I'm a born-and-raised Catholic, I would classify myself as an agnostic, at best.
4.) I'll also admit I skimmed huge chunks of this book. It was the only way I was going to get through it at all. It was worse than I expected.
Things that Bothered Me (in no particular order):
1.) The first half of the book is the father rambling about his illnesses. Yes, I'm very sad the guy had kidney stones and breast cancer and [some other ailment I can't remember]...but I don't see what any of that has to do with the kid getting sick.
2.) If this was all so moving, why did they wait seven years before writing the book?
3.) The kid is 11 now. Don't you think that's old enough that he could have wrote the book on his own? Or at least contributed a chapter in his own words?
4.) Others have said this, but it bears repeating: isn't it convenient that this miracle happened to a pastor's kid? The dad keeps going on and on about how Colton just "couldn't have known" about so much of this religious stuff. Really? Kids are remarkably perceptive. I would find this all much more moving if it had happened to a kid who had never heard "the good word."
5.) The parents only dragged the story out of the kid over the course of years. As a parent, this is extremely odd to me. If my kid started telling me one day he'd been to heaven, you better believe I'd be asking some questions, and right now, not five years later.
Finally (and this verges on a rant), it kind of annoys me how many Christians are saying that this changed their life / moved them to be better parents / etc... I'm sorry...you have the Bible. The WORD OF GOD isn't enough for you? It takes a fairy tale as told by a three year old to convince you that maybe you should get your act together and start acting like a Christian?
Fundamentally, I was just the wrong person to read this book. I am not its target audience. A belief in heaven presupposes a belief in God. Until you can sell me on that, there's not much this (poorly written, highly questionable) book is going to do for me.
ETA (2/2012): I think it's pretty clear I think this particular book is crap. However, if you're interested in first-hand, post-death experiences, I'd suggest reading, "90 Minutes in Heaven". It's similar in its premise--a man dies, spends 90 minutes in heaven, comes back and tells his story--, BUT it's experienced by an adult and told by that same adult. (Unlike "Heaven", which is merely the dad's retelling of the kid's story.) I read it several years ago, but remember being much more impressed by it. I will offer the caveat that I was a much better Catholic/Christian at that time than I am now, so that likely colored my perception of the book. However, even accounting for that, "90 Minutes" is certainly the better written book.