Ask HN: Landing page Vs. jumping right in?

I am building a web application game that users essentially play once logged in. I am curious to know whether or not to use a landing page to explain how to play. If you want to make sure people stay on the page, I would think you would want to instantly through them into the game and provide links for help. But if they don't know how to play, they could just leave so a landing page helps. Of course I could also have a pop up that allows a user to learn how to play or go play on first visit. Thoughts or experience with this anyone?