For example, I've had Deus Ex HR & Batman Arkham City since before Xmas and have yet to complete either of them.
You just had to mention those two, didn't you? I also haven't finished either of them yet...
Or The Witcher 2
, or The Amazing Spider-Man
, or Max Payne 3
, or Spec Ops: The Line
, or Spider-Man: Shattered Dimensions