I was on neurontin several yrs. ago and it made me gain weight like crazy, 15lbs in 2 weeks, and up and up. I have only recently been able to lose some of the weight.
However, except for the weight gain, I liked it. It helped a lot with the pain and made me feel very mellow, nobody could rattle my cage. The trouble was that it would only work for so long and then my neuro would up the dose, this happened every 3-4 months. Then when I stopped taking it withdrawal was a total nightmare. I was sick for days and it took me a couple of weeks to recover.
Of course, just like with any other med, everybody will react differently.