I know this might incite some eye-rolling, but "good" is a subjective term, even in this context. For all I know, a good "math" question could be one with symmetry in either the problem or the solution, or some clever trick that cancels out a bunch of terms (i.e., telescoping sums). Nevertheless, I'll assume that by "good" you mean "thought-provoking."
On this site, I would not trust the "vote" parameter much, for two reasons. First of all, people can vote on a problem they mildly feel is worthwhile, and forget about that particular problem soon thereafter. That action isn't reflective of a very thought-provoking problem. Furthermore, while a "good" problem might indeed draw many votes, it doesn't have to, either. There might be some correlation, but in my humble opinion, it's not a very strong one.
Second of all, there is an incentive for those who like to earn badges on this site to "vote up" as many posts as possible. Sure, MSE tries to hinder this via a cap on how many votes you can do per day- but that doesn't stop some users from just starring random questions, especially if it means getting closer to whatever badge they want.
There is another parameter on StackExchange that I like very much- one that addresses both of these concerns: the "favorite question" star. No one gets any award for starring as many posts as possible, so it's not like there's an incentive to loosely hand them out. Furthermore, starring a question allows you to keep track of it, so on your home page, you're always getting notifications for the development/conversation for that problem and its respective solution.
If you want to see some great problems, look for the ones with high star ratings. And check out the high-vote, high-starred unanswered questions as well. Many of them are open, and very thought-provoking.
TL;DR The favorite-question star is an indicative method of finding "good" questions.