I love having start and due dates on tasks. I love have time estimates on tasks. I love being able to assign a task to more than one person (not just assigning multiple followers, which you can do as well).
It took a while but I've come to love the dashboards. I love the Harvest Time Tracking Integration. I'm begining to love the HubSpot integration too.
After looking at Redbooth, Asana, Avaza, BaseCamp, Jira, Trello, Podio, Wrike, MavenLink, Dubsado, Monday, and more... of the course of years. Many of which I "loved at first" and grew to hate, Teamwork Project is the one I actually like even more today than when we started using it.
Unlike SifterApp (which we otherwise love) and Asana/Trello (which we sort of liked), Teamwork Projects is a full features PM tool with a project space that can keep digital files together (gDrive/Dropbox integrations, or direct upload). Timelines and charts... all the stuff you want for major projects, but it's still easy enough to use.
Two big things. First, I wish the time reports worked properly with Harvest Time Tracking. While you can have both enabled, there is no syncing between the two so it'd but super confusing. Use one or the other.
Second, we have used and loved SifterApp where you can comment and in commenting assign the issue to the next person that needs to act on it. I live tht behavior and am always frustrated I can't do that commenting on taks in Teamwork Projects. You have to comment, and then seperately change the owner, status, etc..
We've bounced through a lot of PM tools, we really feel in love with SifterApp but the lack of a "project space" really hurt us. Teamwork really hits all our needs from records managment (attaching design files, contracts, etc..) and timelines, planning, monitoring and time tracking.