What an interesting thread. From a lighthearted perspective, before I had kids I told myself that I wouldn't be one of those parents who always talks about poo. I used to hate it when my sister in law would go on about my nieces' poo (when they were little, obvs) every time I spoke to her but when you have a baby / toddler it's just a constant feature of your day 
On a more serious note I think I am about living up to being the type of mum I thought I would be before I had kids. I am fairly strict, organised, follow routines, set boundaries etc. They eat healthily, and I limit screen time. I tell them constantly how much I love them and how proud I am of them. We read a lot and talk constantly. I try to make sure they are resilient and like themselves.
But I agree with the others who have been surprised at how mind-numbingly boring small children can be. I don't want to play a game, stand in a freezing park, do jigsaws / craft etc all day. I do it, but it gets boring so quickly. I also like peace and quiet and a tidy / clean house which is tricky with two boys and I find I crave 'me time' massively which I very rarely get, due to husband working weekends and shifts etc. I am also constantly knackered as even aged seven and four they both get up at the crack of dawn and start crashing about which added to bouts of insomnia and anxiety means I feel quite delicate and fragile a lot of the time.
Four-year-old is going through an especially wingey / whiney stage at the moment and follows me about the house constantly which is pretty annoying and I have to try really hard to ignore and not lose my temper.
Having said that, we must be doing something right as they are both happy, confident, kind children and I am proud of the people they are growing into. I guess it's ups and downs / rough with the smooth and I did expect that.