Great product managers know the current customers, industry, potential additional customers, and the company very well. They communicate well. They can optimize the match between customer needs, marketing benefits, internal company priorities, and reasonable developer asks.

The best ones I’ve worked with have been so good that their roadmaps and conclusions feel obviously correct, and everyone has bought into the direction because their input was considered.

The good ones have original thoughts and can combine knowledge from different domains in nontrivial ways