I just finish my interview on Dec.10 (today). They told me the group case interview has been cancelled this year. I think Yvonne and Steven (also Angela and Justin in the reception room) are all very friendly. I didn't receive any challenging questions. Sometimes I felt I spoke too long answers and they seemingly already got what they wanted (or perhaps they found my response boring...) and intending to proceed to next question.
Just be well-prepared to some typcial questions and take it easy.