I don't read a lot of blog, but when I read here are the things I hate about them:
1. Tiny text + Dark background. This leaves me with a burning sensation to close the window and smash my head on the keyboard. My advice: Readable text size (compare your blog to any respectable news website) and clear contrast between font color and background color.
2. A fancy blog template that renders your blog unreadable. Have seen those blogs that have just a 7-word column in the middle of the blog and the rest of the blog is just empty? My advice: simple is better than overly complex.
3. Just videos, pics or links to articles. Coming to a blog to find a series of YouTube videos and no comments is just sad. My advice: a blog is a personal thing, it might make sense to link to an article or a YouTube clip but then I expect you to comment on it or have your own POV about it.
4. Fanatic comment-posters, who would be so insulted by a certain blog post and would leave a stream of hate comments that is, off course, full of profanity. My advice: read the "Letters to the Editor" section in a respectable Newspaper/Magazine, those readers also do make a point, but they do it in a very civilized manner.
5. LONG posts, have you seen those posts that make you scroll, scroll, scroll and then scroll some more?! My advice: think of your post as an ad in your campaign. If you can get your reader hooked on a 30-second ad, it's more effective than a 30-minute ad. All the readers have a million and one blogs to read, not only yours.