Echoes can be a brutal mistress. The game is much longer, and indeed harder than Prime in a lot of respects, and I'm sure that the average Joe will be looking at 20 hours of game time on their first run through. Given the incredible amount of hidden booty (Missile Expansions, Energy Tanks, and Light/Dark Ammo upgrades) that figure will surely be hovering around the 30+ hours mark for those wanting to try for the lofty 100 percent completion record. And also note, you'll need to scan every single critical object in the game to get a full percentage rating for both info and items.