Kickoff Menu Style- Developed by SuSE, will be the standard menu in KDE 4. It replaces the old 2nd generation menu in KDE 3. This is not the same Kickoff that we have available in KDE 3.5.5 and up. Its a port and is instead a plasmoid. I consider Kickoff the best of the 3rd generation menus but Raptor is in development and it will be a 4th generation menu system totally unique to anything else out there. To get an idea of what Raptor will be like go here to see it. Once Raptor is fully developed as a plasmoid it will be an exciting replacement menu.
System Configuration - Developed by Kubuntu, will be standard in KDE 4. This is good idea as the Kcontrol center is a bit confusing. However, the current Kubuntu version does not give access to all KCMs and if we are going to have this as the new means to utilize them then access to them must be allowed. I am not in the mood to use kcmshell setups.
Dolphin will replace Konquerer as the file manager - Don't get me wrong I can see the idea and even the need behind this. However, Dolphin is not KIO capable which means in some ways its a step backwards. If Dolphin is going to be the new File Manager then it needs to be made plugin capable and the KIO plugins will need to be ported over to Dolphin (as plasmoids of course.) Otherwise what's the point?
Plasmoids finally end the issue of kicker applets not being available to all KDE based distros. Plasmoids set and use a standard that makes them plug and play in KDE 4 that does require packaging for specific distros to be used. In other words plasmoids make KDE 4 standards that allow people to use as they see fit, regardless of the specific distro they use. So when Raptor does get released for general use all you have to do is get the plasmoid package and install it into the plugins of KDE 4 and you will have it. That's cool. No more waiting for your distro (or someone else) to package it so you can use it.
Lastly Moodin will become the default splash screen engine, though no surprise there.