Chances are that you've already played Borderlands 2, XCOM: Enemy Unknown, Civilization V and BioShock Infinite... or one of them at the very least. If you've missed out on all four, however, you can grab the whole quartet for £16.00 from Green Man Gaming. Be sure to use their OQE4LG-WEQPSE-SMCME1 for the additional saving.
UPDATE: Not enough? Okay then, why not also have the X-COM Complete Collection, Civilization 4, BioShock and the original Borderlands too!
Thanks to apollolo @ HUKD, both for the original deal and pointing out the four newly-added bonus games in the comments!