Anyway, a rough guide to my rating system...
5 stars (Outstanding): Either a perfect album, or an album where the vast majority of the material is so incredibly good as to compensate for one or two dud tracks. This is desert island disc material, people.
4.5 stars (Fantastic): Really, seriously good, but just not quite good enough to justify 5 stars, either because of a few weak moments, or the fact that I can clearly distinguish this as being not-quite-as-good as an album from the same artist that I rated as 5-star. At least a contender for album of the year.
4.0 stars (Pretty damn good): Pretty damn good. Likely to make my top-10 of the year list (depending on the year). In general, has maybe a couple of absolute stand out tracks and the rest is at least very good. That, or it's a really good album that I just have to be in the right mood for.
3.5 stars (Pretty good): It's pretty good. Might not be an all-time classic, but overall it's enjoyable and probably has a couple of particularly good tracks.
3 stars (Solid): Decent enough. Some very good tracks but at least one major thing that gets on my nerves, possibly eliciting use of the skip button.
2.5 stars (Sonically average): There's some good and some bad, in roughly equal proportions.
2 stars (Sub-par): If I own this it is probably because there are one or two tracks that I really, really like and that's about it. That or it's something that might have been alright at the time but has dated really badly.
1.5 stars (Narf): It's pretty bad but not totally without merit.
1 star (Mostly painful): This CD is probably better suited to life as a coaster. I don't know why anyone would want to listen to it. But then again, I don't understand why people get so gushy over dull indie crap like Arcade Fire or The National. Basically this is 0.5 stars plus another 0.5 stars for a vague shred of hope.
0.5 stars (Avoid at all costs): I would not want to use this CD as a coaster because I would not want people to know that I owned it.

I don't consider it odd that I have a fairly high average rating. I have purchased pretty much everything in my collection (mostly on CD), and stuff that I don't like either doesn't get bought in the first place, or gets traded in. I'm pretty fussy about what I like and don't like, and 5 stars is not something that gets awarded lightly. The upshot of this is a high average rating but a relatively low proportion of 5-star albums.

Also, downrating is stupid.