Although there are a lot of online resources to measure the wuality of your blog, like Blog Juice, Website grader (The bottom of the resports is dedicated to blog) and others like Technorati Authority, all of this services focus on popularity and sometimes SEO aspects.

Taking into account that all a blog is about is people reading your content, the best way to measure your site's quality is to use Google Analytics and check the time spent per visit, and the time spent per page. This way if you see 90% of the visits spend less that 10 seconds on your page, who cares if your traffic is 10k, your blog does not have quality. It may be the design, the content, something that is making the users leave even before they had time to know what it was about.

Time spent on the site, Google analytics graph

As you can see in the image, you have an average, a daily basis, and a visual graph displaying the variations. An ideal time would the one it takes the user to read the article and maybe post a comment. Most users will take about a minute to do all that. If your average is under a minute, then you must do something, go through the stats, page by page, and check how much time they spend on each page, that gives you an insight of what's happening.
Also check the main exiting pages (Which will usually be the same ones they entered) and sometimes you'll see a particular page being exited too much, it is usually because of the article title, an egaging title will keep your visitors on the site, at least long enough to determine whether your article is interesting or not.

Something that is usually a great way of keeping your users on the site is putting an image always on each article. It gives a visual representation of what the article is about, and as you know, an image is always understood faster than a whole paragraph.
Another great way to help the reader know what the article is about is highlighting important words. It helps the user know where to look when skimming through the article.

Follow this simple tips and you'll increase the time users spend on your blog, which hopefully will mean that they will start to read your articles from start to end!