The world champions wrapped up a 3-0 series win with a comfortable 46-6 triumph in the third Test against the tired tourists in Dunedin.
Gatland acknowledged the trip had exposed areas of the game in need of radical work if Wales are ever to end their 63-year losing run against the All Blacks.
“This was very disappointing,” the 52-year-old New Zealander said. “We thought there were plenty of positives from the first two Tests and we started this one pretty well. But it was important we needed to stay in the game and had to score before half-time when we had the opportunity. There were times when our kick-chase was not good enough and we missed a few one-on-one tackles.
“Our tackle success rate was well below our usual standards. We came to New Zealand with a different mindset to evolve our game and be positive in attack. I feel we have done that. But defensively we have been disappointing and have let ourselves down in an area we have traditionally been good at.
“We will take a lot of lessons from what we have learned over the three Tests and we must apply that when we come back together next season.”
It was an impressive start to a new era for New Zealand following the loss of so many of the stars that clinched the World Cup last October.
Fly-half Beauden Barrett scored 26 points, including two second-half tries, with Ben Smith, George Moala, Dane Coles and Israel Dagg also touching down in the rout.
Head coach Steve Hansen said: “It’s a tough time for teams at the end of their season, especially in a World Cup year when they have just gone straight through without a break.
“For Wales, in what was their 17th Test match... maybe some of their guys were already on the plane home.
“They are a better team that that last game. They will regroup and come back stronger for the November Tests and then be a force in the Six Nations.
“But we are happy to win the series 3-0. If anyone had said beforehand that we were going to lose 818 caps and do what we have just done, then I would be happy with that.”
new zealand: Tries: Barrett 2, B Smith, Moala, Coles, Dagg. Cons: Barrett 5. Pens: Barrett 2.
wales: Pens: Biggar 2.
new zealand: Dagg; B Smith, Moala, Crotty, J Savea; Barrett, A Smith; Moody, Coles, Faumuina, Retallick, Whitelock, Dixon, Cane, Read. Subs: Taylor, Crockett, Tu’ungafasi, Romano, Squire, Kerr-Barlow, Sopoaga, Naholo.
wales: Patchell; L Williams, J Davies, Roberts, Amos; Biggar, Webb; Evans, Owens, Francis, Charteris, A Jones, Moriarty, Warburton, Faletau. Subs: Baldwin, Jarvis, Lee, Ball, E. Jenkins, G. Davies, Priestland, S. Williams.
REFEREE: Jerome Garces (France)