I couldn’t answer what’s the best CRPG I’ve ever played, but if you would’ve asked what’s the best story-driven CRPG, things would have been different. While there are some close contenders, Planescape is still heads above the herd. Things start simple, you wake up an amnesiac, trying to find your way in a strange city. From there it gets more complex.
The most notable thing about Planescape is its divergence from the common evil vs good template that is pervading nearly all CRPGs, but to say more would spoil the plot. The amount of text in the game is staggering, at least if you’re not used to reading too much. Planescape benefited tremendously from the already excellent Planescape setting, which is arguably the best D&D setting for including philosophical questions about human nature. Using that as a starting point, the game tells a story incorporating themes of redemption and questions about identity.
When it comes to computer or console RPGs, Planescape is the benchmark to show how high you can reach. But since moments of real brilliance are rare, I’m still waiting for a game to surpass it.