plasma is awesome but default desktop configuration/layout/theme dont show how nice KDE can be, but the bigger issue for me are colors and air/oxygen.

aka :
oxygen: bar looks awesome with composite but widget are plain black so it kinda sux

air: widget look very nice but bar is very intrusive for me and transparency is almost unnoticeable, beside it looks terrible without composite.

menu: plz lancelot default with some kde magic, really the default one looks like a bad merge of kde3 and windows vista menu

widgets: make default some cool applets like a nicer cpu/memory(maybe the one in win7 style ish) info and maybe a nicer clock, but dont just splash big rss widget there.

wallpaper: need more work the default i think here is a distro thing more than a kde thing

colors: this is very personal dependant but i think colors need to be more synced with plasma theme color

this are very stupid issues ofc compared to everything else in kde4 but you know.

i hate windows 7, i tested it well and it have a ton of issues but i have to admit that the default gui settings looks cool as hell, even when kde4 looks better with some magic here and there, for average joe to say wow need something that cool out of the box

i wish i could help you here but im a decent C++ coder but a terrible artist