It is a fact that the Windows-implementation of QuickTime is rather bad because Microsoft have held back APIs and even took lengths to make QT perform worse than Mediaplayer (there are specific functions in Windows that prevent QT from working in an optimal manner - refer to the Microsoft Antitrust Testimonials by Avie Tevanian).

Aside from that, some of the QT codecs are excellent (Sorenson, etc). The abysmal volume control mentioned has also been fixed in version 5 and is now much more convenient (wheel vs. bar).

As a side-node, I have had bad experience working with QuickTime on PCs because of the aforementioned Microsoft-harrasment (sorry for sounding biased, I can't help it. Up/Downvote as you please), while having quite good experiences working with it on Macintosh.