Because I am not perfect I do recognize some of my flaws.  One of them is that I don't pay enough attention to lyrics.  The other big one of attempting to determine "originality".  Also keep in mind that reviews are largely a reflection of personal taste.  If you like Deep Purple's The Book of Taliesyn, that's fine.  When I refer to Black Sabbath as the "drugged out, Satanic younger sibling of Led Zeppelin" don't take personal offense.  Nobody's opinion is any more right that any other.  Hell, that's what makes music fun.

As for the ratings themselves - the main line that I have is ***1/2.  To explain, if I consider an album good and worth listening to all the way through that is the worst rating it can get.  That's not to say albums with lesser ratings are not worth hearing, but one should probably skip some parts.  The real key to how I review is based on songwriting.  If you write good songs, but play OK you're going to do well.  If you waste your fingers playing crap it's going to hurt you.  Here's the general rundown:

***** - Flawless.  This is really hard to get.  There is some leeway, but not much.  For example, King Crimson misses the mark but having a pointless noise collection in their first album.  Pink Floyd likewise unwisely allowed Roger Waters to rhyme on their first album for a song.
****1/2 - Almost Perfect.  Usually this is an album that misses out on a 5-star rating but a small goof up.
**** - Solid Entertainment.  Maybe it's not perfection, but either good musicianship or good writing (or both) can elevate an album to this level.
***1/2 - A Good Time.  The watershed mark, as discussed above.  Overall it's enjoyable, although some parts may not be as strong as others, or it's derivative.
*** - An OK Time.  This tends to be from unevenness.  A good example is the Move's Shazam, with really good songs, and then boring, repetitive filler.  Bad songs hurt too.
**1/2 - Worth a shot.  Maybe there's a couple of good songs, but the rest is just boring, boring, boring.
** - Yawn.  Maybe one good song, and the rest is junk.
*1/2 - Ugh.  That one good song isn't so good, and the rest is absolutely abominable.
* - Terrible.  Nothing is good, nothing is right, and I regret having spent a dollar on this.

So, even though this most likely won't help much there it is.  It's also important to realize that because I make some pretense at objectivity for a task that's inherently subjective the ratings are not transferable.  That is to say, what is a ***1/2 album for one group would not be a ***1/2 album for another group.  The truth is that I think some groups are better than others for intangible reasons, and in the interest of fairness they get lower scores.  This doesn't mean that mediocre albums by lesser bands are going to merit 4 stars, but it does mean I will surprise myself sometimes, like on that Aerosmith review.  ***1/2 stars, who would have guessed?  Other web sites (see below), like George Starostin's have artist ratings to help show what role the band's identity plays in an album rating, but as this is a album, not band-oriented site I don't have the patience to tease my opinions out and then quantify them, at least on that aspect of reviewing.

Why do so few albums receive the lowest ratings?  Mainly because in order for the music to have been released some record label had to approve it.  They draw the line somewhere.  If I were to record 65 minutes of fake fart noises that would merit absolutely no stars because it would be devoid of any artistic merit (probably anyway).  Occaisionally stinkers do get released, because the label is desperate or the band has been having success up to that point, among other reasons.  Albums that are technically impressive but barren of songwriting talent (usually in the form of no hooks) tend to get **, as they lack the most important aspect of music (in my opinion).