So the second one is worth playing? I've heard mixed opinions

It's a jarring transition, especially if you play them back to back.

FFX has light-hearted moments but overall it's tone is very serious. The combat system is a traditional-yet-robust turn-based affair. The ending is tragic, and Yuna should be heart-broken.

FFX-2 opens with Yuna as a pop star singing a light jpop beat. The combat system involves dressing up three cute girls into different outfits with Sailor Moon-style transformations when you change job classes. It's almost a parody of the original; I'm fine with that idea in theory, but this serves as a canonical sequel to a very dark game.

Your opinion of X-2 is going to depend entirely on how much you can get over this weird transition and appreciate what it does well (like, for example, one of the best job-class systems in the series).