This logo is bad for many reasons. First of all, the man looks frightening to me, and I would not want to go to him to work on my teeth. The font is very outdated and looks like it is from the 70's. The red color with the yellow background is also uninviting and harsh. It is very unprofessional looking and would not make me want to go there.
This logo is good because it is not too complicated and is a nice simple logo. There are two d's which represent Darrow's Dental. The words also work well together and are spaced nicely. They also line up and work off of the size of the box on the left. It seems clean cut and professional, which is something I would be looking for when going to a dentist.