Well, according to me anyway.

EXPECTATION & PRESSURE
It must be hard being an All Black and having that legacy at your back all the time. But, this time the expectation looked to be too much. It started wit the Lions victory bu that portentous Adidas ad set the tone for the nostalgia-needy NZ public but then they went and gave the players dirt to take with them to France. Dirt - I ask you! Dirt from the grounds of the all clubs that supplied the ABs. Jeez, way to ramp up the expectation and leave the guys in no doubt what's at stake.

It's easy to forget that these players are still just kids. Even the senior players are young men in real terms and most of them have only ever known rugby. What must it be like to be told that a few weeks in France would define the rest of your life? Win, and you'll be a champ forever. Lose, and you may as well leave NZ for good. This kind of expectation leads to unacceptable pressure and I believe the AB's game suffered for that.
It suffered at the death on Saturday because the ABs seemed incapable of winning ugly when it really mattered. Again, the expectation from Kiwis is that the team has to win playing a game no one else can play. It's OK for England to boot over a drop goal but for the ABs only glorious, multi-phase tries will do. The expectation pf 20 point wins and champagne rugby meant the MiB couldn't contemplate anything else when the chips were down.

UNDERDONE
Bart has talked about this on the front page but for me the lack of gametime for the squad didn't mean they weren't battle-hardened or soft in any way. They looked as if that essential instinctive ness Kiwi rugby players have had been eroded by not playing footy week in week out. Where was the wide-eyed kid with the widescreen vision that took the Lions apart in Wellington. Gone. Carter had been replaced by some robot in silver and black. Same went for a lot of the guys. They looked like they were going through set move after set move instead of ripping it up naturally. They should have been given game time in the NPC and S14 and let the injuries sort themselves out.

PEAKING & LACK OF SETBACKS
Yes, you peaked.
Just like England you peaked a year early and in the intervening period other teams caught up. England had enough of an advantage to win in 2003 and NZ should have had the same this year but failed by two points. You were still better than France but got derailed.
The journey was a long one too - maybe too long. England managed to deal with the four year build up mainly because we were kept honest by successive 6N failures. In contrast, the ABs have scarce had a bloody nose in the four years since Sydney. It would have done you good to have lost the Bled or even the Lions series in the overall campaign to win the RWC. But that's not your fault. You can only play what's in front of you and the sad fact is that you weren't tested enough.

CRUISING
Back in my day, we had an old expression: 'When you're cruising - you're losing'. And when in front on Saturday, the ABs took their collective foot off the pedal. It gave France some hope and that was all they needed. Another score and it could easily have been all over.

THINKING TOO FAR AHEAD
I honestly feel the ABs went into the RWC fixated on a revenge semi against Oz. You forget that the only way to get to the semi was through the QF. That's what tournament rugby is all about. It's called knockout for a reason. There was a lack of focus on the job at hand. Using England as an example again, we had a horror QF against Wales in 2003 but managed to regroup at half time and tough it out. In that sense, half time was an important element of that game for us - it provided a point where a line in the sand could be drawn. In contrast, the ABs had to do that thinking with the game in process - much harder to do.

LEADERSHIP
I honestly think you missed Umaga. Not only would he have solved the issue of who to play in the midfield he would have provided the big character the ABs so obviously needed when the chips were down. All the RWC winners have had these guys. Pienaar with SA, Eales with OZ and of course Johnson with England.
McCaw doesn't look to have the same qualities. He couldn't change the script when it mattered. Don't get me wrong, great player and almost certainly a great bloke but he doesn't strike me as a natural leader.
Johnson, during that 2003 QF, famously pulled his team together and said bluntly: 'This stops here'. Would or could Ritchie have done the same? I don't think so, not in the same way as Umaga might have. 

ARROGANCE
Having stuffed France so many times in the run-up to this RWC, the ABs clearly thought normal service would be maintained. But in doing so, they forgot one important factor - France.
The Frogs are from France for a reason - it makes them fucking French! They do what they like, when they like. If they want to win, they'll give it a real good go. If they aren't that bothered, they'll lose by 40 points.
They are annoying, unfathomable, idiosyncratic fucks at the best of times, but put them in a situation that appeals to their over-developed sense of romantic drama and they will stuff you.
Maybe 1999 was too long ago for this group of ABs or maybe it's because you don't have to play them every year in the 6N but either way the easy wins of recent memory meant that the ABs went into this game thinking it was a done deal. Wrong.

Of course, there were other factors why you lost - including in some part a forward pass. But for me the above is as good a set of reasons as anything else I've read or heard.