I really like KDE, except for the one aspect: the task manager.

I'd really like the ability to actually rearrange the tasks.

In any case, I think it's generally just not that well designed. Is there a replacement maybe? One that doesn't make minimized windows gray, for example, and generally looks nicer (Windows 7 has this configured pretty great).

in task manager settings change sorting to manual

for grey icons try systemsettings -> app appearance -> icons advanced -> all icons (or just panel) -> disabled -> set effect -> no effect

Also with regard to the "disabled" or "grey" appearance of certain windows in the task manager - try changing the Plasma theme you are using (as a quick test) as it often influences the appearance of elements in Plasma such as this as well.

systemsettings -> app appearance -> icons advanced -> all icons (or just panel) -> disabled -> set effect -> no effect

i had some problem few a months ago but i forget for this solution