Just to add, forms generated by the jBPM Designer have JavaScript validaton built in which is based on the Object types of process variables that you specify in your process BPMN2. They also have some CSS stuff to make them look "pretty".
The down-side of forms generated by Designer is that they all follow the same template. To change anything in the forms, you would have to edit them manually. Creating different templates for the generated forms is pretty easy, and if needed would be really cool for community to contribute some new ones and I can make them pluggable in Designer. For existing tempaltes see here: https://github.com/tsurdilo/process-designer/tree/master/src/main/webapp/taskforms
Hope this helps.