I found the 3.5 year gap massive, but maybe because I already had 2 with a barely 2 year gap who were thick as thieves. They loved the baby like they would have loved a puppy, and liked to spoil him and tell me off if I was ever cross with him - but his closest in age sibling didn't play with him as a peer until he was about 4, and even then the older one was very much in big brother role, letting the younger win although nobody ever suggested he should etc.
I guess it depends on the kids. My eldest of 3 still mentions frequently that she'd like another baby sibling, but I've told her she'll have wait til she's grown up and have her own children now, or hope her uncle has kids one day...
I liked having siblings growing up even though I was never especially close to any of them, and one of them was an absolute nightmare who played my parents like fiddles with crocodile tears to get her way and get me in trouble if I didn't dance to her tune. However my mother was a very intense woman (not nasty, just incredibly emotional and demanding) and I was always aware on some level that my siblings diluted her!
I also liked the noise of a full house/ lots of people around the table. Despite, or perhaps because of, not being a "people person" I always appreciated the fact that its less demanding and intense being one of several, than an only in the spot light.
Despite not being close to any of my siblings in adulthood I am glad they exist to diffuse the intensity of my parents expectations/ disappointments/ emotional needs.