42% is pretty good for gaming. Look up some of the numbers on other titles -- when BioWare originally posted something about ME2's completion rate before this year (it was something like 49%) they were absolutely ecstatic. 42 is still pretty good.
Red Dead Redemption is a completely different kind of game, granted, but to give a good measure of how much this stuff really matters, its completion rate is 10%. And they used the same definition -- not 100%ing the game, just beating its main story path.
Eidos, when speaking of the Hitman series' stats in this regard, has claimed that 20% is average. :P