RE: stars and DL counts, I'd say the best measure is checking the creator's other repos, their number of followers and the issue churn rate. Stars can be useful but only as a very rough process of elimination.
If the project appears to have several active contributors that would be good too.
I'm a star inflater and I feel a little bad about it. AFAIK GitHub does not have a good "bookmark" mechanism besides stars. So when I come across an interesting/useful project I'll start it to be able to find it later. My browser bookmarks have become a bit of a black hole where URLs go to get lost.
So hopefully I didn't bookmark a project someone else is trying to judge the quality of based on stars. Who knows how much technical debt or damage I've caused because GitHub doesn't have a bookmark feature that isn't gamified.
If the project appears to have several active contributors that would be good too.