Way too many games these days have hidden items that give you permanent bonuses, be it a heart container, a weapon upgrade or whatever else comes along. Rewarding exploration sounds nice but in the end it hurts the game in my oppinion. You see, when a game has permanent rewards (i.e. they apply for the rest of the game) you end up crippled for the rest of the game if you miss them so you have to search every nook and cranny and by all means avoid progressing through the level before you're done. I hate that, it makes me spend more time on searching treasure than actually playing through the game. A game with no permanent collectibles simply allows you to blast through without worries about missing anything, without having to think "did I look everywhere?" before going through the exit door. Less worries = more fun.
This only applies to linear games of course, a game where exploration is a part of the regular game completion can hide as much as it wants to, just a linear game that never has you go back to any spot forces you to be extra careful about everything.