This is really a tough question, everyone is different and pain is highly individualized, but a pain medication is considered successful if it results in a 40-60% reduction in pain levels. The object is never to remove all pain, it is to restore some quality of life, so you can think about something other than the pain and get some sleep.
My medication relieves most of the burning and reduces the muscle pain in my legs to a fraction of what it would be without meds, but I still have numbness, pins and needles in legs, hands and arms, a feeling of constriction in my feet and ankles like they are wrapped in a tight bandage, feelings of things running up and down my legs, and a variable amount of burning. These are constants. Then there is breakthrough pain when the nerve pain in my legs just becomes hard to take despite the long-acting meds. Many of us are never really comfortable, but it should be possible to find significant relief.