Not sure why, but after not touching GTA IV for nearly 2 years, I cannot put it down.
 
No, I didn't start the story over and, no, I haven't purchased the DLC (I will soon though).  
 
For some reason, I can't put down the multiplayer.  What I once found to be a dull experience because of auto-aim, juvenile opponents (and teammates), and GTA IV's often tourettes-inducing version of the Euphoria engine is now an incredibly enjoyable experience.  There's just something about jumping your motorcycle off a ramp into your buddy's passing speedboat that other games can't match.
 
I would write more, but my hands need the sticks again.