In music, I almost exclusively rate what I own, and by extension only music I like. In films, I'm more systematic and have rated a good many things I've disliked strongly and have a more even spread of ratings, though I am generous there to things that interest me in one way or another, perhaps beyond their actual quality. If you want to know the music I don't like so much, I direct you to almost the entire genre of metal, very little of which (that is not Motorhead) would be able to garner more than 3 stars, or to my list entitled "No."

Music rating scale:
5 stars = I can listen to it any time and find myself loving it. Important to my development and very possibly important music in general.
4.5 stars = a terrific listen. Thorough enjoyment without that extra magic something to push it to the top.
4 stars = lots of great music here. Solid all the way through or several stellar cuts surrounded by more pedestrian material. Often my "starter" grade for records I like right off the bat before I get to know them better and mark them higher or lower (or not), so there are a lot of these in my collection.
3.5 stars = problematic in one or more ways, but I still find it enjoyable (or at least parts of it). Usually this is a good one to read my review because you may find more (or less) of worth than I do if you understand where I'm coming from.
3 stars = deeply flawed with sparks of interest or a well-crafted piece of blah.
2.5 stars = an aesthetic misfire. Something poorly conceived and thus not liable to attain any great level of quality no matter how well made, or something poorly executed to the point where its potential positive qualities are obscured.
2 stars = bad. Dumb or poorly made without being fun enough to compensate.
1.5 stars = bad, and probably something that offends me. I don't own any of these and thus have not rated any as such, but I could find examples upon request.
1 star = anger-making music. Something that I physically cannot listen to for whatever reason and that makes me more than mad, where I cannot intellectually process my reaction to the music.
0.5 stars = nothing has ever been this bad. I am saving this for the worst thing I ever hear in my entire life. I can imagine it - morally, aurally, and aesthetically offensive - but the reality would have to be worse than even that for me to use this rating.

Film rating scale:
5 stars = Masterful. A film full of ideas and with artistic execution to match. Fires on all cylinders, usually under the guidance of a director who thoroughly understands the interrelations of light, movement, color and sound (when present), framing, and other intangibles.
4.5 stars = Great. Completely worthwhile viewing, generally a major artistic accomplishment or superior entertainment.
4 stars = solidly made entertainment or an artistic statement rendered with some flaws or longueurs.
3.5 stars = Reasonably well made and worth a view for its good points, though the less good parts may drag the whole down if you can't forgive them.
3 stars = Interesting ideas rendered inertly, confused ideas, and competent entertainments with no spark belong here.
2.5 stars = Flawed at some fundamental level, but not necessarily without interest. Possibly a good scene/element or two, but rarely more.
2 stars = Not made without skills, but definitely made without holding my interest. Very probably annoying.
1.5 stars = Aggravating for sustained periods of time, with very little light of good stuff breaking through the cloud.
1 star = Exceptionally offensive and/or poorly made.
0.5 stars = Bad ideas, poorly rendered, and not good-bad, just shitty-bad.