I guess it does come down to how each player tackles exploration. For example, I will always explore everywhere I don't need to go first - within reason, I don't go off trundling to areas way above my capacity - and I will explore every inch of ground. For me, the reward is the world.
What I think Bethesda does well is include little backstories to the areas you explore, so while you may get a new weapon as a reward you'll also discover - through the environment - that somewhere was a vampires abode or bandits were smuggling drugs or something.
And maybe many will disagree with me, but I thought Baldur's Gate did a good job of this too - and this was something severely lacking in BG2.
There were the odd wilderness screens that had little in them (I'm thinking the roads to Nashkell) but the majority did have unique features. A lake with a fisherman's lodge perhaps, an old ceremonial circle (with a crazy Cleric) or random encounters from adventurers. They were the punctuation for exploration.
And while we're on the subject of exploration, I don't want to be limited. Obviously some limits do need to be in place to stop you visiting story-based areas. Again, BG1 did this well. You save when you visit a new screen and, if it turns out you are underequipped or not a high enough level, you return when you can.
If that means failing, so be it. Games these days don't seem keen to let you fail - and I can understand the reasons why - but I want to overcome adversary, not deal with it.
