I do like that a top-level datatype in basecamp is the milestone. Todo lists, message, files, specs, etc. can all be included as part of the milestone. On the negative side, the one feature I was looking for -- a hierarchal view of all the workitems for the cycle -- seems to be missing.

Quoted: People working together on projects need a way to share project data. There are emails, meeting appointments, assigned tasks, and files to share among project members. In addition, appropriate access must be granted to internal managers and external stakeholders such as clients. While Microsoft Project, Project Server and Project Web Access are designed for complex enterprise projects, many organizations and project teams don't need the sophistication of Microsoft Project, and do not want to manage and administer such a system