I just accept all the free games they give me. Even if I don't play them now, I may in the future. I imagine it like opening a time capsule some years into the future, opening a massive library of games I've rarely touched.
My most played freebie on EGS is DEATHLOOP, pretty incredible singleplayer FPS with cool time loop mechanics from Arkane. I haven't tried the multiplayer mode yet, where one player is trying to hunt you down as you complete objectives or vice versa. I also put a good couple hours into Dead Island 2 after finishing the game via Xbox Cloud gaming a few years back. These are the perfect type of freebie games to me, ones I'm interested in but don't want to spend money on.
The only time I played a game I got for free on EGS then bought it on Steam is Death Stranding. Lots of Death and Dead in these game names.