After all that R&D $$$ the YZ450F rides like a YZ250 but doesn't start nearly as easy!
Hey, I am a 2 stroke fan too. But I will tell you, it starts easy enough. The first 4 kicks, when cold are needed, I am told, but I am not a recent 4 stroke rider, and it always started for me on the first or second kick.
It is fuel injected. Don't touch the gas - Stick to the routine. It seems harder to stall in a corner, but that is just my impression. I never killed it where I might have stalled my 07 450.
If you are a 4 stroke rider, I don't think you will find it anymore tempermental than any other 4 stroke. If you are a 2 stroke rider going to a '10 YZ450, you might be in for a shock.
It is alot faster than a YZ250 and turns better. That is just my opinion, but I have ridden both. That should be worth some R&D $.
I will always ride 2 strokes, but don't knock it until you've tried it.