National/ACT have definitely opened up a lead of around 5% in the last month or so. But that is a very slim lead, especially when the margin of error is considered.
Probably the most similar election to this in recent times is 2005. I definitely think the chance of a polling error (either way) is higher than usual, because there are probably a few more swing voters than usual. We're also seeing stronger support for the smaller parties than almost any other MMP election.
Even if the polling is accurate, the election could turn on a few events/policies, again in either direction. And there's the NZF factor - it will definitely make things "interesting" if they get above the 5% threshold.
Anyway, my view is that National/ACT are favourites right now, but it's still anyone's to win. It's funny how a lot of people seem to assume that it's more or less a forgone conclusion!
Edit: another piece of trivia - the last 6 Prime Ministers who took office during the parliamentary term have gone on to lose their next election. So Hipkins has some history to overcome!