EU4 is £9.
If you like Civ5 but are a grown up then buy it, and buy it now. I have ~500 hours logged on the game and many more spent offline, it is brilliant.
Stranded Deep might also be worth picking up for £7, pretty much Castaway: The Game. Age of Empires 2 for £2.50 and Fallout New Vegas for £2.50 are also both excellent deals