Installation of KDE is easy, emerge kde-meta, however, not everyone wants everything that kde-meta includes. I would like to propose that the kde-meta include a few USE flags, such as 'education', 'scientific' and particularly 'games', such that, setting of use flags will not install unwanted apps. The alternative is to unmerge kde-meta and manually install each required sub meta package, exlcluding the unwanted meta packages.
You should try to make a minimum use-flags. Therefore this is not an alternative but the expected behavior.
Please read description of kde-base/kde-meta. If you want a modular kde start with kde-base/kdebase-meta and add applications or other meta packages afterwards. For more information see: http://www.gentoo.org/proj/en/desktop/kde/kde4-guide.xml
