I'm a new father (4 weeks). From the pregnancy, to the delivery, to the first smile, to the every morning warmly feeling of having created life with my love one, it is all about love and sincerity. We are already thinking about a second one...
She is a wonderful, and I love her to pieces, but goddamn this is a trying experience.
However, there is another difficult period around 2-3 where they rebel against your authority, and it is a constant battle to reassert control. On one hand, they have more motivation, more time, more energy, and fewer distractions. On the other hand, it's usually 2 vs. 1, and you control the food and entertainment.