This is something we see - patients who are happy with a drug yet doctors want to change their regimens - quite alot and I'm not sure why. Vicodin, Morphine and Methadone are schedule two drugs which all are similarly restricted by the government. 

Methadone has growing acceptance as a pain drug although it does have the stigma of being used for opioid dependence sometimes. Methadone may actually be more effective against neuropathic pain than Vicodin and it doesn't need to be dosed as frequently as some other opioid drugs. Its also possible it may cheaper and it does have reduced addictive properties. It's not a bad drug to try out. 

if you do switch to methadone you have to be careful about starting up slowly on it. 

From what I've read Morphine appears to have a higher addiction rate than other opioids.

I would ask your doctor exactly why he thinks you should switch. It would be good to get clear on that.