There were "a tonne" of elements 343 Industries wished had been improved while making Halo 4, Frank O'Connor has said - and he's pledged to "do better next time".
But overall, O'Connor remains proud of what he called "the best" game in the series.
In a retrospective post on the Halo Waypoint blog, he praised how the 343 had filled the "oversized shoes" left by series creator Bungie.
"We altered the engine. We expanded the universe. We innovated in storytelling, technology, and even marketing," O'Connor wrote. "It wasn't flawless by any stretch of the imagination, but by most objective criteria, it was a resounding success.
"So we know we have a lot to do. And we know we have a lot to learn. But we also know that we now have the capacity, the teamwork, the technology and the experience to do much better next time."
343 Industries is currently working on Halo 4 DLC and, beyond that, a next-generation Xbox Halo game.
"There are a tonne of things we wish we'd done better [in Halo 4]," O'Connor continued. "Features that didn't make it into the final game. Glitches that emerged. Missteps made. DLC fiascos. Communication breakdowns.
"We now have the capacity, the teamwork, the technology and the experience to do much better next time."
Frank O'Connor, 343 Industries boss
"But there were things that went astonishingly well - the creation of a genuinely competitive AAA studio chief among them."
The team has stated that Halo 4 is just the first in the franchises' Reclaimer trilogy. 343 Industries is set to see Microsoft's shooter series through games five and six at least.