Overview: HR doesn't do their job, nor are they competent. Hiring managers and the actual employees doing the interview seem to be much better.
My experience in interviewing with this company actually began several years ago. When I first applied, I received an invitation to come interview on-site. However the HR coordinator there did not seem to grasp that I had a busy schedule and could not come in at a whim. There was no phone screen prior to set up of a meeting, purely through e-mail which seemed to cause some problems. 2-3 e-mails later, they were still unable to correctly respond to my e-mails for scheduling and I decided to forfeit the opportunity.
Couple years later, I ran into this company again having forgotten my experience. Another HR recruiter emailed me (at my work e-mail which is not listed on my resume) to set up a face to face interview; so once again no phone screen. This time they were more accommodating to my scheduling, so I did the on-site interview.
Some advice I would say is to arrive a bit earlier at the building than you'd expect. They actually have security you have to go through including metal detectors and a lot of visitors show up and can take up precious time. Plan accordingly.
The actual interview with hiring managers was fine. There is a personality test that others mentioned (that personally seemed to be a waste of time for me).
It was a 2 round interview, meeting with some of the senior members and some of the team members. Everyone seemed ok, but the cultural fit did not seem to mesh well with me. The hiring managers also needed to sell me more on the position and company.
They need to work on their recruiting process, HR definitely needs work.