Given the recent discussions around strategy games thought I would mention that CKII is now f2p on Steam having previously been b2p.
No CKII is not a "failed game" that has had to add a cash shop it is simply marketing. CK 3 is due to launch late 2020. It also has multiple DLCs that can be bought individually or in bundles - its been out some years now. So this is marketing.
You don't - however - need any DLC to play what is arguable one of the very best games of its type. (Most DLC adds different regions and time periods.)
If you decide to give it a try my advice to a new player would be to remember you play an individual not a country. And whether you start as a simple baron or a great emperor your "score" will be based on whether you "improve" your lot in life. Also remember that all other characters you encounter - wife, husband, children, most trusted aide - are all played by the AI as individuals; with their own aims and objectives. They may help you to greatness or decide you are an obstacle.