I like the Prima Guides, but I don't use them as guides. Mainly they serve as bathroom reading material and books for my little brothers. That is the market they should hit. Little boys will read about games, and the guides serve perfectly.
For tips and such GameFaqs or Wiki's are better. Mainly because they get updated, while the guides are static, this is especially an issue because so many games have DLC now. The Oblivion Wiki was a lifesaver for me, because it filled in so many 'huh' moments. Additionally, many wiki's have bug pages and mod links, solving problems with the game as well.
For tips and such GameFaqs or Wiki's are better. Mainly because they get updated, while the guides are static, this is especially an issue because so many games have DLC now. The Oblivion Wiki was a lifesaver for me, because it filled in so many 'huh' moments. Additionally, many wiki's have bug pages and mod links, solving problems with the game as well.