Big emphasis on their core values - read up on the 5 Zero's before your assessment day! You only interview with a senior member of the company (department may vary), there's no separate technical or HR interview.
The rest of the assessment day consisted of: company presentation, group exercise, situational judgement test (written), interview, lunch, presentation exercise
NOTE: The HR department is VERY willing to give feedback on your assessment day, so take advantage of this. I didn't get an offer, but this is because of a recent visa policy.