I have had them all, the 9000, the 9700, Storm 2 and now the 9800
Beside the bigger screen compared to the 9000 the resolution aint better. The screen is good, movies look great but beside bigger not much better.
Sound is great... volume is good. Absolute the same or better then the 9000. Typing is a different story, I found out that most of the times I do not open the slider but only use the screen keyboard. Only when I have to type a long mail I use the slider keyboard.
Overall, I am very happy with this new model. It looks sexy, it works smooth. The 6.0 software is really amazing good!
So, the 9000 is a good phone... but the fun factor for this 9800 is really high. And beside the fun it is still a good quality phone!
Hope this helps you to choose ...