It would be impossible to say why Neurontin works better for you than Lyrica. Both are anti-convulsants. The exact way Neurontin works is unknown. Lyrica works by affecting the chemicals in the brain that send pain signals throughout the nervous system.
Each patient reacts differently to any given medication. This is why it is so important to try different medications if one doesn't work. Even similar drugs will work differently in different patients.
Regarding one statement made in a previous answer: While neurontin can cause severe depression, it is a rare side effect and is certainly not applicable to everyone.
Karen