I certainly can describe DNSimple as an ultra simple DNS Service full featured with backed DNS configurations for many common applications like Gmail, Tumblr, Blogger, etc. Those "backed configurations" follows the 'next next finish' principle which is very handy.
Also, DNSimple counts with a 'new' record called URL which allow Heroku users uses their CNAMES pointing to domain's root. i.e. foobar.com pointing to foobar.herokuapp.com. So, if you're a Heroku user, I can surely recommend to you move to this service. This is the most important and liked feature in my experience with DNSimple.
DNSimple price is very accessible. Only few dollars/month without domain limit. When you join, there is no raise in price as days go by.
In comparison with Amazon Route 53, DNSimple wins with its simplicity, stable and almost awarded features (like URL DNS type) and fixed price.
If you use VPS, like Linode, you'll have a great improvement from Linode's DNS manager. Without Domain Limits, DNSimple turns a great option for Linode users as well.
For simple users, like bloggers, youtubers, etc, DNSimple will guide through wizards to help you setup your domain and connects it to your service. This way you can have the fastest configuration done than ever.
There is no analytics panel available. This may deal breaker for some DNS power users.
Also, there is no ping tool to keep your domain available 24/7 based on ping response time (Time to Live).