Q: Strange braking issue.

I recently replaced the master cylinder and brake booster (http://www.getdiscbrakes.com/j84315672) and brought the vehicle to a mechanic to replace part of the brake lines. The mechanic also claims he bled the system. The problem is when I step on the brake pedal there is almost no stopping power until the brake pedal is almost to the floor at which point the brakes engage and the car comes to a screeching halt. The problem is significant enough that the vehicle is not safe to drive. I believe the problem may be air in the lines but don't understand why there would be such extreme stopping power when the brakes finally engage. Is there something else I should be looking at also?

Note - except for the parts mentioned above, the entire brake system is all original with front and rear drum brakes.

My car has 88000 miles.
My car has an automatic transmission.