I'm right there with Inspector Spacetime for the most part. Except, I'm surprised everyone is seemingly missing this... that wasn't meant to be a "happy" ending. The only people who "grew" were Shoshanna and Ray, because they were the only ones who made tough, evolved decisions. Hannah is back with Adam, Marnie is back with Charlie, and Jessa is again traveling, just as she was at the beginning of the series. We're basically back at square one, and that was the intention. The whole point was to show that most of the girls didn't evolve. They each got so close to actually changing and maturing, only to revert back and rest on their laurels at the last minute.
In her conversation with Laird, Hannah finally came to the realization that she had to be the one to take of herself, but then she welcomed back Adam to take care of her instead. Marnie should have moved on as well, but instead retreated to someone who represented her old life, when she had it all together. Those final moments weren't meant to be legitimate "fixes" from the creators of the show. Depiction is not endorsement. Instead, this was Girls' take on The Graduate. Those were mistakes being shown in the final montage, purposely put to a "rousing" romantic score, playing off that whole trope in ironic fashion. The girls got what they want. But what they want isn't what they need, and I thought that was brilliantly depicted.