The most useful feature of grails is that it allows me to use groovy instead of java, which makes my code more efficient as compared to java. Also, I like the flexibility in creating domain classes, GSPs, controllers, etc., which can be easily integrated with each other. Sometimes it takes time to set up the project but once you have done, its very easy to work with. I would recommend everyone who wants to create an enterprise grade web application should go for this tool. I am solving problems related to data access, security, user interface and business logic.