Fifth release doesn't mean it should be more mature. Look at the upcoming Windows Phone 7 OS. It might be "7", but it's definitely not going to be as mature as 6.5. It's actually a whole new OS. Shoudn't even be called Windows. =P Very similar story with Fremantle. Does Maemo5 look like Maemo4? Did Maemo4 have phone capability? It's not a whole new OS but it's quite close from what I've read.

Your comments about you really liking the phone etc just doesn't match up to the harch title of this thread from what I can see. Nokia didn't fail with N900. Definitely not. or even you would have sold it already.

I guess you can say Nokia should have released N900 when it was fully mature as you want it. If so, we might never have seen it released. I'm glad Nokia released it last year and let the community assist in making it the best mobile device out there. It definitely was the right decision imo.