1. That looks good?
Needless to say that if the theme does not convey a professional image (and if a professional image is important to you), do not use it, even if it means you have to go with another theme that does not do all of the above.

Looking for that perfect theme is a bit like shopping: try some out, see what looks best, and have fun with it!

2. Simply Unique?
If you try to create a visual brand with your blog, then try to avoid using the default WordPress theme or another theme that everybody and their dog has been seen in several other blogs.

Try to find The Best Free Wordpress Themes For Download that are not used in an excessive number of blogs, or get a custom theme developed if you are willing to hire someone.