Please try to avoid simply saying "this app is accessible" or "this app is not accessible".
Instead, think about the kind of information that you find useful when browsing the App Directory. Think about anything you have learned whilst using the app that might help other users.
If the app is inaccessible, then give some indication of the problems. Some others might decide that they are willing to try and work around the problems that you have identified.
Also, the developer of the app might see your comments. Knowing what problems you encountered gives them a good starting point for addressing any accessibility issues.
Knowing the extent of any accessible issues can also make it easier to see if future updates of the app fix these problems, or actually introduce new ones.