The ideal hot questions list would present the best posts of the network that are of interest to a wider population than only experts on that subject. The hot questions are shown to a much broader audience than the source site alone, showing them very specialized posts that they won't understand is not really useful.

I think drawing some attention to the larger SE network is one important role of the hot questions list, but I don't see recruitment of new users as its main purpose. It raises awareness of other sites that the users might not have noticed otherwise, and ideally it showcases some good content, and that might lead to some users staying on the site. But the whole mechanism is not targeted enough to be very effective in that regard, the hot questions list is shown to a large population where only a tiny part is likely an expert in the subject of one specific site. I think the best ways to recruit new users need to be targeted, e.g. recommendation from a colleague or a link to the site in a place frequented by experts on that topic.

The hot questions list becomes problematic when it identifies questions that are popular, but are not really of a high quality. When the algorithm identifies a question where the community of the source sites thinks the content is not very good and maybe even a bit embarrassing for the site, there is a problem. The questions should have popular appeal, but they should still be something even experts are not embarrassed to have as a showcase for their site. Often an excellent answer alone can raise a mediocre questions to something that deserves a place in the hot questions list.

So what the algorithm should identify are questions (and their answers) that are considered good by the source community, and of interest to a much broader audience. Looking at how many users click on entries in the hot questions list is a good way to judge the broader appeal, I think. But I also think that the quality aspect needs to be considered as well. The best way I can think of to examine this would be to look at the difference in voting between users active on the site and users that arrive at the question from the hot questions list. If the source community votes very differently than the "outsiders" looking at the question, this might indicate a problem.

What is the Goal of "Hot Network Questions"?
As a non-native speaker, I do not fully understand the meaning of the term "to become controversial" in the following text, which I have to translate into German:


  Where translators have made their presence felt they have become controversial, with those who characteristically intervene, seeking to domesticate texts, contrasted with those who foreignise, supposedly allowing other languages to alter our own.

