Having kids will change you, no question. You would throw yourself under a bus to save your kids, absolutely. But let's not forget that you are still an individual with aspirations, ambitions, needs. Even after your child is born. Some people are better than others at repressing that side of their identity, instead evolving into a seemingly completely altruistic being. I couldn't.
The first year with my first born was hard but still magical (plus my wife stayed home with him so it helped a lot). After that, time to be used for myself was coming back, restful nights... Piece of cake.
Then I pushed for a second child (I always loathed the idea of raising an only child for some reason). My wife had resumed working by then and it was understood that she would go back after a couple of months of staying home with the baby.
That's when it became insanely painful for me, trying to protect my newly returned freedom (after my first born became more independent) while carrying 50% of the child rearing load with a newborn and a toddler.
I had to surrender (my self lost) for my own sanity and the well-being of my children. The lesson I think I've learnt is that to be as "successful" as possible at raising kids (whatever that means) you have to let go. A lot at times. And hope for the best.