Do you like to travel? Are you adventurous? If so, it is sooo much easier to travel around the world with only one child! Easier AND cheaper of course! Also you have more free time for yourself as you and your husband can take turns more easily to give the other parent a break.
Your child will most likely have more resources - financial and emotional from her parents. She/he will probably be very confident, mature and social.
I was an only and so is my husband. We love our only child and love life with an only, that said, we decided to have another because there are also some disadvantages to being an only, which do not come into place now because you asked "how great" it is

There are positive and negative for both op!