Some key points of caution for current Australian visa holders is that if you hold an Australian visa that is not included in this arrangement you will need to apply separately for a New Zealand visa. See: New Zealand's entry requirements.
Another important consideration is that your Australian visa must, allow re-entry to Australia after your trip to New Zealand. Thus single-entry and some bridging visa holders must get relevant re-entry approval prior to departure from or re-entry into Australia.
Australian visa holders also should take note that while New Zealand will grant a visa for up to 3-months for the event, the visa will not have similar rights as their current Australian visa.
To see if the visa you hold, or are applying for, is included in this arrangement see: Eligible Visas for ICC Cricket World Cup 2015. To determine whether the temporary visa you hold is part of the trans-Tasman arrangement, see: Eligible Visas for ICC Cricket World Cup 2015.
International visitors will still be required to meet the respective health, security and character requirements of both countries and each country will retain the right to refuse entry if a visitor does not meet these requirements.
For further reading:
http://www.immi.gov.au/event/wcc/Pages/cricketworldcup-frequently-asked-questions.aspx