In advance of the latest expansion, Lightfall, releasing next week, player's logging in to Destiny 2 are being greeted with a notice that the last expansion, The Witch Queen, is free to play through the weekend. This is similar to last August, when previous expansions went free before the latest season release. And like previous instances, any loot collected in the free period will be available to use after it ends and the content is again locked out without a purchase.
In my Witch Queen review from last March, I stated that this was "the best game state it has ever been" and have found it largely moving from strength to strength this last year. There is a lot to do in Witch Queen, more content than the game has ever really presented. My advice for those jumping in would be to focus on the exotic weapons. The Parasite heavy grenade launcher is a quest that appears after the main story line, a story which is also excellent. So grind through the story and go for the Parasite and any other cool weapons you can get your hands on. Like Osteo Striga which can be an absolute monster on Warlock builds paired with Necrotic Grip or the Dead Messenger which gives you a special ammo grenade launcher capable of cycling through Elemental classes, adding a lot of versatility especially when playing weapon locked end-game content like solo lost sectors or Grandmaster Nightfalls.
Destiny 2 and its expansions are available on the carious digital marketplaces for Playstation, Xbox, and PC. Witch Queen is even on sale on the PS Store through the week after next if you want to keep grinding through after the free trial is over.