You say "he is portrayed as vindictive and unforgiving". I see that as sort of a non-believers interpretation of the OT. I don't see any big change in personalities. I just mostly see a change in the context from dealing with building a literal nation from the ground up, set apart to God, to building the spiritual kingdom of God since the people he chose strayed from the path.
In fact, in some ways it could be argued he became more strict in the new testament. OT=do not commit adultery. NT-if you even look with lust you are guilty of adultery. OT=thou shalt not murder. NT=if you hate your brother you are subject to a murderer's judgment. OT=honor your mother and father. NT: If you love your mother or father more than God you are not worthy of the kingdom.
The "wedding guests" i.e the bride of Christ that he invited in the OT, the jewish people, chose on their own accord not to show up for the party so he went out into the streets and invited anyone who was willing to come feast with him.