The Good...
The Integrated Brasero for CD/DVD burning is nicely implemented and everything generally feels more speedy, and the boot-time is quicker and neater, I like the new splash screen. Dual desktops worked straight away after I installed the Nvidia drivers, unlike in 8.04, which took a little jiggery-bodgery. I also like the new Remote Desktop applet that shows available remote desktops with one click of the icon.
The Bad...
Kubuntu has abandoned Amarok 1.4 before version 2 is ready and fully featured, although you can still install 1.4.10 using this repository. Last.fm still didn't work for me in Amarok 2 and the gui feels cluttered. As with 8.10, I still don't like the default network manager although I have now found out than you can still install the old one. More annoyingly to please newbies, Ctrl Alt Backspace is disabled. This is an Xorg change rather than Ubuntu specific, and it is fairly easily changed.
...and the Ugly
The default brown theme looks a little better and though I'm still not keen on it, it is easily changed (and is the first thing i change!) Also in the latest Gnome, it is missing two of my favourite themes - Glossy and Clearlooks classic.
overall I am pleased with 9.04, much more than 8.10, and I'm running the 64bit version (I've not noticed any 64bit specific bugs as of now) on my main desktop machine.
