Splinter Cell: Conviction will take 12 hours to complete on normal says the game's creative director, Maxime Beland, in the latest issue of OXM. There will certainly be a harder difficultly level for folks that are into trial and error for 30 hours, but the "normal gamers" will get a well-sized adventure. Beland says this was done because he wants people to actually finish the game. That's quite a good idea.
Also, at around 12 hours of gameplay, Badass: The Game won't wear out its welcome -- if it keeps the action going. Of course, there'll be multiplayer to extend the experience, but we likely won't be able to crack skulls in urinals there ... or maybe we will, which would then confirm Splinter Cell as game of the year.