The interface is clean and neat. The installation is fast and smooth. I installed Kubuntu 10.04 last night. I was pleasantly surprised.
Some of the new features include Grub 1.98, plasma support, removal of HAL, and so on. If you like Ubuntu, you will love 10.04.
Personally I always have a feeling of missing half of the things I need when I use Ubuntu. I miss su, Administration controls, and various little things that are readily available with Fedora builds.
I still test most of the major versions of Linux when they release. Some releases are ready, some feel rushed. some are just not ready. 10.04 Lynx feels like it is ready. 10.04 is a Long Term Support version. This means updates will be available for a minimum of three years for the operating system.