Roo is a productivity improvement tool, which is user friendly and automates generating generic code and configuration required in developing Java enterprise applications. I would really recommend using Spring Roo once before writing it off.
Also, you only need to know about AspectJ, Maven and Spring to use Spring Roo. The code generation strategy followed by Roo makes it a very unique development tool. You can customize generated code, the code follows best practices, there are no runtime dependencies of your application on Roo, you can remove Roo by using Push-in refactoring, you can write add-ons to extend Roo functionality, and the list goes on and on.