Excellent player with every possible video format supported. I use it for watching movies, I use Winamp for audio.
What I like? Nice sound/picture effects, like normalizer, crystalizer, postprocessing... A lot of settings for subtitles, picture size... I don't think a setting exists that isn't included in The KMPlayer.
What I don't like? Often web streams (audio or video) don't work, although it's said that it's supported. Picture quality is a little bit lower than other similar programs, like VLC.
But overall still the best video player there is!