"They certainly came at us pretty hard and were able to knock us off our lengths. Credit to them. But we've got to get better."
McCullum reckoned Trent Boult and Doug Bracewell will benefit from the match, and he batted off criticism of offspinner Mark Craig, who conceded 234 runs in 45 overs for three cheap wickets at the end of Australia's second innings.
"Mark has done an outstanding job for us ... We've seen in the past he gets better as tours go on."
McCullum liked the way the batsmen, notably the outstanding Kane Williamson and openers Tom Latham and Martin Guptill, handled the Australian attack. Williamson scored "probably the best hundred I've ever seen from a New Zealander in the time I've been playing".
McCullum was sawn off by an awful umpiring decision from Englishman Nigel Llong on 80 today, but had no grumbles.
"Both Nigel Llong and Richard Illingworth are two of the best umpires in world cricket, who are allowed to make the occasional mistake."
Australian captain Steven Smith singled out his team's new ball bowling as needing work.
And he gave left armer Mitchell Starc a verbal clip round the ear after he threw a ball
back at Mark Craig in frustration today.
"I thought it was pretty disappointing. He's done it a few times and I will have a word [with him]."