Flash, if done well, can look very pretty, like these. Flash Player, as a web audio-visual delivery system, has many advantages over Java, Acrobat Reader, QuickTime, RealPlayer, and Windows Media Player, mainly because of its "almost instant" play characteristics. Anyone who has used Windows Media Player knows that he has to stare at that "buffering..." indicator for some agonizing seconds before the video starts to play. With Flash Player, the buffering time is significantly shortened.
Flash is not universally liked, however. The advertisers have abused the technology and made those annoying bandwidth-hogging ads we cannot seem to avoid, unless you turn on the "Adblock" device in your Firefox browser.