From the sounds of it, you play the game twice - once on 'normal' for the story experience and once on 'hard' collecting all the knick-knacks. You may want to play the game again for the gameplay, but normally replay value comes from unlockables, 'levelling up', online, and actual features only available from multiple play-throughs. IMO. For example, I've played through CON at least a dozen times, playing different character classes, using different builds (such as that game allows), and with different play-styles. That's enormous replayability. I played ICO once and that was that - bottom rung replayability. UDF is clearly nearer the bottom of that scale.