Nemo, I think this is about your experience with your Mother, and while I'm sorry you had that, I'm pleased that you're not actually horribly judgemental about parents who don't instantly take to it.
I think one of the things you have to accept is that you and your Mum are not the same people; clearly you have strengths that she doesn't have (not slating your child to their face would be one of these).
I'm in a similar but completely different position to you; my Mum, Sis, and pretty much everyone else in the family all took to parenting like ducks to water. I found it a real struggle. They didn't martyr themselves to their children; parenting simply came naturally to them and they enjoyed it. When I had my babies, I expected it to be the same but I found it totally different. I struggled with breast feeding (made me depressed and nauseous, felt like fingernails down the blackboard) so switched to bottle from 6 weeks. I can't sit and do nothing in front of the TV; I have to knit or do sudoku or crosswords - all not possible with a child who wants to be held constantly. I didn't get on with the sleep deprivation and struggled to nap in the daytime. My brain itched with boredom.
I didn't get PND until pregnancy No2 (well, 4 really but I lost the middle two). That made a bad situation worse.
Yes, of course I felt like a failure; especially when considering how great every other Mother was. I longed to go back to work.
Over time, I have learned two things. One is that my Nan hated parenthood too. She loves her children, but found it hard; especially when they were babies. She was a secretary in the days when mothers were expected to give up their jobs and go home to cook and clean. She hated it. It appears that this isn't unusual and it's only how you handle those feelings that can make it 'wrong'.
The second thing is that different parts of parenthood are easier/more difficult for different people. Sis, who I'd considered as a perfect mother found the ages of 8-12 really hard. The children suddenly had social lives and things to do that excluded her and she felt bereft. Mum says she really struggled with the teenage years; she had 4, 3 of whom went through puberty in totally different ways but at the same time. She said that at the time it felt like she'd used all her patience up when we were small and just wanted us to grow up already.
So I didn't like babies when they were in their larval form. I bloody love the toddler stage though. This post has taken an hour to type, not just through length but because I've been breaking off to make mosaics with the 4yo. I love the clay and mess and creativity they have now. Husband struggles with this being a neat and rules person, but he knows he's going to enjoy other bits more.
It's all OK. It's all parenthood and while it isn't wise to tell your children how hard they were; it's also not wise to assume that everyone can do all of it perfectly, and that everyone enjoys the same stuff.
Sorry for length.