Shadow Warrior! I saw it online for £10 so thought I'd give it a go, ended up being one of my favourite games I've played all year. Chopping off demon heads with a katana in a Japanese temple is pretty fun.
Plus completing heroic difficulty is one of my proudest gaming achievements, insanely difficult and only 150 of us have managed it on PS4 leaderboards.
The Talos Principle is really good too, loads of super hard puzzles in it and you feel so good when you manage to complete each one!!