My first real exposure to anime was Akira in 1989 when I was in highschool. I managed to watch a couple different anime while I was in college, but it wasn't until 2004 that I really started to watch anime seriously.
I usually dont read manga, and what I do read is because I want to get a better look at an anime that I thought was really interesting or to continue the experience after the anime series ended.
When I rate an anime, I'll give it an initial 7, and then move it up or down during the season. The final rating will come after the final episode. First, it gets a temporary final rating and then I cross check it with previously watched anime and see where it falls within similarly rated anime. I adjust if necessary, then give it the final permanent score.
If you look at my list you'll see very few low rated anime. I generally enjoy most of the anime that I have watched. Anything rated a 6 and over was an enjoyable experience for me. So an anime really has to work hard for me not to find some redeeming value.