Metal Gear Solid. Played through them all apart from 4 because I never had a PS3. 2 is probably one of my favorite games of all time, and in terms of gameplay, Phantom Pain is up there as the best.
Bioshock another series I love. The first one is obviously the best, but I love Infinite. I think Infinite was treated a little unfairly when it came out, but it seems to be more appreciated now.
Resident Evil. I think I've played through all the mainline games apart from 7. Played some of the spinoffs including the awful Resident Evil Survivor. One of the worst games ever made.