More than anything it was just a terrible interface.
The interface that is shown on the website is not the actual interface, it's a Flash app and looks like it hasn't been updated for about 10 years.
They have been working on a new version, but it seems like they have been working on it for quite some time now. Some features of the "Platinum" (non-flash) app were slowly being rolled out when we left, but the bulk of the app was still Flash. We stayed with it for about 6 months, and finally moved away from it about 3 or 4 months ago, this year.
I'm sorry, I know that's not very specific or concrete, I only tracked time to projects and couldn't stand it, but it was collectively hated throughout the company, especially by the PM's.
I'd suggest staying clear, or definitely do the trial before committing. Asana has been a breath of fresh air for us.