I tried them and in my opinion: trying all three is definitely worth it, to experience their gameplay and see the history. Since it is free, it will not cost you much and if you play as far as you like, you will not lose more than 20 minutes per game.
However I was not good enough to complete the games, so I read the story here and then watched the mandaloregaming videos about the series. And I adore what they did! They pioneered so much in FPS games and the rampancy idea is brilliant, as is Durandal.