Yeah, I'm with the other ladies on here.
Going from 0 - 1 was a huge learning curve for me, so I didn't find it easy.
Going from 1 - 2 was also difficult, because the demands two placed on me. Though, somehow I did find it a tad easier.
Going from 2 - 3 was the easiest adjustment. He slotted right in, and like the previous poster said, the eldest 2 played while I tended to baby. There was a big gap though (they were 7 and 4). It meant I didn't need to do much for them. By this time I also knew how quickly everything passes, so on difficult days I just soldiered on.
Going from 3 - 4 was a bit more difficult for me. I'm older, and the eldest 2 have so many things going on that I feel I'm always on the run to fetch or drop them at school, or busy helping them with projects, homework or studying. Sometimes I wish I can just hide away with baby for a few months, and just concentrate on her and no other children in between. It's getting easier though, now that she's in a routine and can sit and play for a while.
I've never (personally) heard of someone regretting having nr 3, but I've heard from loads of people how they regretted not having that last, 3rd one.