I love that it's easy to use, I can just click a button and get an email address. It's relatively cheap (you can pay as little as $5 per year if you want). The interface is pretty straightforward and intuitive. It's not very customizable. I wish I could set up multiple domains for different purposes. Also, the support is really bad.
They don't respond to tickets or messages. If something goes wrong, they will simply tell you to contact their "support team" which has no idea what they are…