What are some effective ways to measure the success of your product development efforts as a PM?

User feedback, KPIs, time to market and cost effectivness :)

Track user engagement or conduct a user feedback sessions

User Feedback, Pricing Test

I would like to add review of marketing ROI metrics

Besides what's already been listed here: feature adoption

1. Your customers are proactively providing you with negative/positive feedback about your work/product/feature. 2. You might have back-end usage data available, pull that data and dig deeper to see what and how the customers are using your product. 3. Surveys. Find out whether your customers actually care or use what you're spending your time and efforts on.