Ask HN: Programming book recommendation features

I've been mulling over building a site that provides recommendations for people looking to buy a programming or software engineering book as a side-project.

This topic ("what are the best books for learning X") seems to always come up again and again on StackOverflow, HN, reddit, etc and I think the current options for book recommendations and searching are pretty limited. I don't think the 5-star model really works and I want to try my hand at making something better (e.g. a 5-star rated book may be well written, but not suitable for beginners). And trying to google "X programming book" often leaves you frustrated by spam and no closer to finding the right resource then when you started.

So, what things do you consider when picking out a new book? What information do you wish you could filter by? How do you decide between a large set of similar options? I have some ideas already, but I wanted to hear some other opinions.