There is 17 months between DS1 and DS2, then 20 months between DS2 and DS3.
Personally for us it's fantastic! Specially when DS3 was born the older two happily played together whilst I was feeding or changing him. They always liked to be included to like passing up the burp cloth, passing wipes or nappies and generally asking questions.
DS2 is now taller than DS1 so I get oh are they twins ALOT! Pretty much each time we are at the shops their is atleast one person who will ask. DS2 and DS3 have talked early even DS3 walked before he was one he was so eager to get up and race about with the other two!
Of course one grows out of the terrible two stage another pops in though lol.
Older two share a room I think it's going to be harder to separate them in a new home eventually. The boys hate being apart which may be a downside when DS1 goes to school next year.
I spend one on one time with each of my boys DS1 loves learning and is doing excellent with learning to writing numbers and letters. DS2 loves pretend play at one stage he thought he was a robot so I always pressed his bellybutton ad he'll talk like a robot which made us giggle alot. DS3 is a night owl, so after the other are in bed he gets alone time with mummy and daddy. He is more clingy and still shares our room.
May be a busy household but I wouldn't change a thing.