One factor which tended to make the stepfather transition even more difficult was the age of the children. Stepdads seemed to have more difficulties when the children involved were teenagers. So I took careful note of what worked and what didn't in these blended families with teens.
To be sure, there are important challenges facing stepfathers with teens.
Resentment. Teens who have experienced a divorce or the death of a parent tend to be pretty resentful of their situation in life. Whether they lost an in-home dad by death or divorce, it is easy and natural for them to focus that resentment on someone they perceive as being a "replacement." Also, teen stepchildren will also often make the comment that "Mom married you-I didn't."
Bruised Feelings. After losing their in-home father, teens may experience not only feelings of loss but also of rejection. They will often be hard-pressed to develop, or even be willing to entertain the thought of, a new relationship with a man. In addition, many teens feel that their family that included them and their mother was "just fine" before you entered their life. They may see Mom's remarriage as failure on their part to meet her needs. In any case, stepdads face an uphill battle with these kinds of feelings.
Hope for Reconciliation. I suspect most children of divorce secretly hope or fantasize about a reconciliation between their parents. Mom's marriage to someone else is a stark dose of reality that puts an end to those hopes and fantasies.
The Father. If your new wife was divorced, the children's father will always remain a factor in your new family. He is the primary parent; you may be seen (or may feel) like an interloper in this relationship. If your wife was widowed, the memory of the children's father can also be a major challenge in developing a new relationship with the kids.