There's still a few hours left to pick up the best video game to have ever been made in the age of man at €15, so I'll assume that'll be around the £12-13 mark in the UK on Steam: Far Cry 4.
Far Cry 3 is €5 and FC3 Blood Dargon (stand alone game, pretty damn funny and good in its own respect) is €3.74. So in pounds... yeah knock off about 15% to 20% I suppose. FC3 was my favourite game till FC4 came out.
I'm a sucker for beautiful single player open world action games where I can conquer a map, meet the best villains in video gaming, have a full freedom in weaponry and tactics and bla bla bla, and Far Cry is pretty much the best at that stuff.
Oh and tip: don't even bother with that caveman arcade game that they slapped a Far Cry title on. The least fun aspects of Far Cry games is to hunt animals and scavenge stuff, in FC Primal they made a whole game around those things. So no guns, no trippy drug missions, no proper objective and utterly uninspired villains. The only thing FC Primal is good at imo is graphics and its degree of immersion. (black jaguar = best pet you can wish for, i'm drifting off here)