To stay on topic: I don't like demo's, I look at previews and reviews to know wether a game is worth the money or not.
so you rely on opinions of strangers?
thats actually not a very good idea!
If you read multiple (p)reviews, you can form a general idea about the game. Reviewers often tell how certain aspects are worked out(i.e. combat, magic system, storydepth) and even though the reviewer may not like a specific aspect, you might. I don't base my purchases on scores or percentages, I just try to find out how different aspects of the game are handled by reading multiple (p)reviews so I can make my decision to buy a game or not.