The ones that start looking at their kids as "obstacles" or "things that are holding them back from stuff." The parents that want to maintain a lifestyle similar to when they were childless (mad free time, no obligations, not having to be responsible for another person, can be spontaneous, etc.)

The parents that I've seen embrace home life and parenting look like they do fairly well (I mean, kids are gonna get on your nerves no matter what). The ones that don't seem like they have a lot of up-and-downs.