Alan Wake is among four new games joining Xbox Game Pass for PC throughout the remainder of this month. It'll join the service on May 21 (ie, today) alongside the return of Cities: Skylines, and Plebby Quest: The Crusades. The latter is a turn-based strategy game "set during the crusades of Europe and the Middle East". It's been received well on Steam.
In addition to the above, Minecraft Dungeons will join the service when it launches on May 26.
As for the games leaving the service this month, on May 29 you'll lose access to #IDARB, Brothers: A Tale of Two Sons, Hydro Thunder Hurricane, King of Fighters '98 Ultimate and Old Man's Journey.
Alan Wake will be well worth a revisit. It celebrated its 10th anniversary this year, and hasn't aged poorly at all. To check out what else is available on the subscription service (which is still in beta and still $1 to join), this page has you covered.