The only way to get a good job out of this is to do a floating mud floor.
We do this over any concrete slabs where we install tile.
First, goes down a 6 mil plastic, then hardcloth/ wire mesh 2x 8 foot sheets or similar, and last goes the mortar based mud job. Find your high spot, and float it with a 12 foot straight edge from there.
Basically this lets the floor move by itself and not let the cracks and dips show up telegraphing through your floor from below.
And don't forget, as Neal stated, you need to control the water from comming in at the old door openings.
Hope this helps, you can get more great advice from John Bridge, he is a guru for sure.