Just make sure you do it before November 18th, because once the promotion end, the game will likely go back to its old price.
To celebrate the first year of Destiny 2 being available on PC, Blizzard is allowing fans to redeem the base game on Battle.net for free for a limited time. Keep in mind, only the base game is free, but this does include all of the balance and economy changes that have happened since launch. Those who already purchased the game on Battle.net will be eligible to receive an exclusive gift of their own: a special in-game emblem marking the game's anniversary that will be available in December. After November 18th, players who claimed their free version of the game will be able to keep it forever.
Additionally, all Destiny 2 players will have access to the Destiny: Forsaken PvP/PvE hybrid mode, Gambit from November 9-11 during a Gambit Free Weekend. That said, all Destiny 2 players can try out the Gambit DLC this weekend. According to PC Gamer, you'll also need to activate Blizzard's SMS Protect 2-factor authentication before you can claim the game. During this period of time, Battle.net users can claim Bungie's shared-world sci-fi shooter to own.
The system requirements are pretty tame for Destiny 2.