What does Basecamp do well? Basecamp is a good creative collaboration tool between clients & agencies.
What does Basecamp not do well? Basecamp is only as good as the information in, and usually doesn't replace emails and other means of communications among teams.
What do you wish you had known about Basecamp before using? If the team isn't committed to using it over another service, it won't solve the communication/timeline issues that may have lead you to seek out Basecamp in the first place.
Have you used a competitor to Basecamp? If so, how does it compare? We use RingCentral for inter office communication and meetings, in addition to Office 365 for file collaboration.