Can doctors tell me what does the pain feel like after scoliosis surgery?

Hard to answer: The pain after surgery varies significantly among people. Factors include age at surgery, magnitude of surgery, pre-op pain status, co-morbidiites, etc. Some patients go home without taking any pain medication at all although that is not the norm. Most people need some narcotic pain meds for a few weeks post-op.

Quite severe: Usually quite severe - cramping / pressure muscle and incision pains. Depends on the extent of the operation and how much bone resection and soft tissue dissection had to be done.