For me it’s either Splinter Cell Chaos Theory (lot of different ways to play through, getting stealth rating’s to 100% and just very satisfying game) or Uncharted 2 (linear but amazing campaign, replay value mainly just experiencing those wonderful moments again and again, but also looking for treasures and different difficulty settings).
Re4 og, Dino Crisis 1-2, Re3 Nemesis due to the different paths like Dino Crisis 1, and more recent one, The Last Of Us Remastered