Not free, but quite good sales on fps games on gog.com right now:
gog.com/…/deus_ex_human_revolution_directors_cut
www.gog.com/en/game/bioshock_remastered
www.gog.com/en/game/bioshock_infinite
gog.com/…/the_outer_worlds_spacers_choice_edition
www.gog.com/…/fallout_4_game_of_the_year_edition
www.gog.com/…/fallout_3_game_of_the_year_edition
www.gog.com/…/fallout_new_vegas_ultimate_edition
www.gog.com/en/game/metro_franchise_bundle

Personally I really enjoyed Deus Ex: Human Revolution, the Outer Worlds and Fallout New Vegas. The others aren’t bad either but those three are my favourites in the list.