I was surprised at how well DS adjusted to the change, we had a ridiculous first few weeks, when DS2 was in NICU, and DS1 got shunted all around the place, but he did so well, and loved DS2 from the first moment that we brought him home.
The most annoying part is the hitting and the pushing, and (today) the standing on the baby, He doesn't do it to be malicious (the standing was simply because the baby was in the way and he wanted to get over him), he just can't seem to control himself, and I noticed that his 4 YO cousin does it to his baby brother too. No matter how many times he has time out he just doen't seem to get it
I found DS1 so hard as a baby because I was so busy stressing, that I'm really enjoying DS2 as a baby, I definately found the first 6 months hard, but now its really great.
Also I think any less love the oldest child gets from you, they will get in spades from their new sibling.