In doing our research, we often encounter designs that look good and, at first glance, seem to address UX needs just fine. But as we get into the testing we uncover unforeseen or just unexpected difficulties that could have, or even should have been addressed before the design go the go ahead. This can be anything from colors not contrasting enough, to navigation items labeled wrong, to text being just too small to read.
Here’s a great checklist from the guys at MYPLANET to help you through all those questions.