--are not quite as regulated as I think they should be; often, the "inert" ingredients vary considerably from one formulation to another, and as far as the "active" ingredients go, up to 20% variation is allowed.

So, you may have a point in noticing a different effect, or not quite as good symptomatic relief, upon switching to a generic.

I do know we've had a few people over the years report that they did not seem to be getting quite the symptom relief on generic gabapentin versus an equal dose of Neurontin. And at times, the variation also occurred between different manufacturers of gabapentin.