What do I love about having my boys:
Being able to go to first screenings of Pixar films without anyone giving me a funny look 
Watching them do things for the first time - I amazed myself that I could sit and endlessly just watch them both as babies, marvelling at how wonderful they were.
The loveheart eyes - happens when they're only a couple of months old, they just look at you and you can see virtual lovehearts coming out of their eyes at you. Such an adoring look - never see it again though, not in the same way! :(
The funny things they do, the funny words they say, the little noises of happiness - DS2 has had a full-on "numnumnum" day while eating today, and he's 2.9! Just love listening to him enjoying his food like that.
Getting to play with toy trains again
Watching them when they see things for the first time - the perfect O of their mouths, the wide eyes, the excitement!
Playing in the leaves in the garden
Blowing bubbles
Christmas takes on more meaning again
So much. Of course there are downsides, when things aren't as easy as you'd like - but they bring so much fun and joy as well that it makes up for it.
I really really loved the tiny baby stage, because I co-slept and breastfed, so didn't have to get up in the night as much as people who don't do those things (except for nappy changes of course!) and therefore wasn't as tired as some people get, so I really enjoyed this. Up until 2, I couldn't be happier with them - but after 2, they start to get a bit more independent and resistant to doing as they're told and then they're a bit more frustrating!
But the joy when they curl their arms around you for cuddles, or snuggle in for comfort, or tell you they love you, or "you look booful, mummy", makes up for it. 
And I wasn't that keen on the idea of having DC at all - if I'd married someone as ambivalent about it as I was, I doubt I would have had any, so I'm glad I married DH who wanted children, else I'd have really missed out!