The most prominent feature that differentiates GamePass is the day 1 releases. Gaming journalists hyped this up as Sony's version of GamePass, when if you've actually be reading between the lines, was never going to happen. Sony never positioned this as a direct competitior ie. Like for like feature parody with MS.
Sony were never going to launch Horizon : Forbidden West, GT7, or GOW Ragnorok into the service at launch, and anyone expecting them to had unrealistic expectations. Sony has mentioned before, that that type of GamePass model is unsustainable for them. That's why we are seeing Returnal and Miles Morales launch into the service ; As they have made most of the return of investment from the games already.
It also sets an expectation of what could launch in the service going foward. A curated list of PlayStation Studio games from the previous 12-18 months (Among the other partner games). I think it's a good balance of value. Ultimately, it comes back to whether I see value in the extra 40 Euro per year, or an extra 60, and what additional benefits Sony wil offer. We have no idea on the list of legacy PS1, PS2, or PSP games will comprise of yet either.