Are the robots we create alive?
I didn't like it when it first came out. I thought it was just a flashy rehash/mangling of a lot of cool sci-fi concepts from William Gibson and others, and the "battery" premise was a complete turn-off for me. But I dug the sequels, and eventually softened my criticism of the first one and now I really dig all of them.
Yeah, why humans and not electric eels? And electric eels wouldn't require a ton of processing power to provide a simulation environment...
I found Dark City much more gripping, and creepy in the 'what if it's actually happening?' kind of way.