The way I score my list:
10 - Brilliant. Loved it from start to finish. Exactly what I want from an anime and much more.
9 - Drew me in from the start. Thoroughly enjoyable, usually particularly strong in at least one aspect be it characters, plot, etc.. A personal favourite.
8 - Provided more than I wanted. Entertaining throughout, maybe a few dull parts.
7 - Got what I was looking for, nothing more nothing less. I found it entertaining, but nothing special.
6 - Didn't get what I was looking for, but not necessarily bad.
5 - Fair, neither particularly good or bad.
4 - Poor, not terrible, but generally didn't enjoy it.
3 - Bad, didn't like it. Possibly liked a few bits here and there, but generally gave a bad impression.
2 - Disliked a lot, definitely not my thing.
1 - Reserved for the worst of the worst, unbelievably bad. Terrible story, dislikeable characters and insulting.
These are very subjective scores and are largely if not solely based on my own enjoyment of the series. I also find it very easy to enjoy most of the series I watch and will in most cases only pick up series that I think I'll like.
100th anime - Black Rock Shooter
150th anime - Usagi Drop
200th anime - Pokemon: The Origin
250th anime - Monogatari Second Season