One of my greatest joys in gaming is the feeling of discovery one gets from exploring a finely-crafted world. When a world is designed properly, it can really suck you into its setting, and when you have the unrestricted freedom to explore its boundaries, you get a strong sense of place in the environment. It's not merely the sightseeing that makes exploration compelling -- it's the rewards you receive for your discoveries, whether they be little treats left by the developers or just the psychological gratification you get for finding a more efficient path.
Some of the real fun, however, comes from discovering tricks that the developers neither intended nor anticipated, like backflipping into an exploding bomb to reach a high ledge in Ocarina of Time, or planting mines on a wall and climbing up them in Deus Ex. These discoveries are more fascinating to me because they're completely unscripted. As rewarding as it can be to bomb a cracked wall in The Legend of Zelda and find a wealth of hidden goodies inside, it's really just a scripted sequence designed to happen in a precise way. There are obvious clues telling you what to do, which make these discoveries a little less personal and a little less dramatic.
Exploration plays a prominent role in non-linear, open-world, free-roaming sandbox games. Much of the appeal stems from the player's freedom to go off and search for adventure in his own way, but some games promote and reward exploration much better than others. Playing Risen 2, I've noticed that the exploration is at times very creative and satisfying, and other times it's rote and boring, which got me thinking about the broader picture on how games can design worlds that beckon for a deeper, more personal level of exploration and discovery.
In Risen 2, you need a lot of glory (experience points) to increase your stats, and a lot of gold to learn skills with trainers; consequently, your character development is always restricted by a lack of these resources. Map exploration is an integral element of the character progression system; there's always a modest-but-steady flow of gold and glory from the weaker monsters populating an island, but there are always special rewards tucked away in discrete corners of the map. Exploring each island to its fullest grants you a lot of unique rewards which grant permanent boosts to your stats, or give you a lot of resources to upgrade yourself the conventional way.
Skyrim has similar rewards for exploration (reading the cover page of a book to increase your stats), but more often than not, these rewards don't feel that rewarding to me. Oftentimes you get a boost for a skill you never use, and the reward does nothing to improve your character. Even when you get a skill boost for something integral to your playstyle, it ends up feeling more like random luck than something offered as a direct reward for your actions. The size of the world map is just too large, and there's so little of value to be found in great stretches of the map, and so it often feels like you accidentally stumbled into a reward, or the game spoon-feeds the rewards to you through the "radiant story."
With Risen 2, the islands are large enough to give you that open, sandox feeling, but small enough that they can fill them with a lot of worthwhile detail. In Skyrim, a lot of the landmass only exists to spread everything out; in Risen 2, every square foot of the map is worth exploring because, for the most part, every treasure is worth finding. Virtually every single stat is useful to any kind of playthrough (you never receive completely useless bonuses), and with attributes limited to a maximum of 10 (and requiring a lot of glory to increase them at later levels), even a single +1 boost to an attribute is immensely valuable.
Where Risen 2 misses the mark, however, is in limiting the explorable spaces of the map. In a departure from other Piranha Bytes games, you can no longer swim or freely climb any surface, which restricts the explorable spaces of each island to essentially flat lands, with a lot of small boundaries. A lot of places are clearly visible and yet basically out of reach, and since the exploration is designed to happen on the flat lands, when you do stumble into a seemingly obscure, hidden recess of the map, there's never anything rewarding to find there. Instead, you're just left with a realization of "Oh, I guess I'm not really supposed to be here," and it subconsciously trains you not to explore anywhere outside of the obvious spaces.
For the most part, exploration becomes more of a tedious effort of time-consumption as you systematically move across the map, just making sure you've been everywhere. There's rarely any sense of self-discovery, as if you discovered some hidden jewel somewhere to make the experience more unique to your own personal input. Rather, it's kind of like being inside of a dungeon in a Zelda game, looking at the map, and just sequentially visiting every room you haven't been to yet. And in the rare cases when you can climb somewhere to find visibly hidden areas, there are always rock shelves jutting out from the face of the cliff -- practically the only climbable surfaces in the game. So the only hidden areas have completely obvious clues telling you where to go.
Some of the best moments in Gothic 2, by contrast, come from exploring well off the beaten path, into obscure, hidden areas. Imagine my amazement when I climbed up onto a ridge that, by all outward appearances, looked like a useless bit of background scenery, and found a human skeleton propped against a tree with a rare crossbow, a few bolts, and some gold coins on the ground. At first I thought I was being clever by exploring somewhere that other players would be unlikely to discover, and then felt a rush of elation at finding a unique reward waiting for me.
It's even more satisfying to use the terrain in some creative way to get into a locked region before you're supposed to be there. In Gothic 2, there are several areas of the world that you're not supposed to go to until certain points along the main quest line, but if you know where you're going (and want to get some extra items, equipment, and experience long before you gain access to these areas), you can usually find some clever way in and reap all kinds of rewards to make yourself far stronger than you should be by that point of the game.
These little tricks allow you to explore the game world in ways the designer never intended, which makes your experience more unique because you're taking the train off the rails and doing things your own way. Instead of just following the pre-determined paths, or just sequentially visiting every marked destination on your map, you're carving your own way through the game world. There's also a more satisfying level of feedback for this kind of exploration, because your rewards and accomplishments feel like they stem more directly from your own actions, since there's a lot of content you never would've experienced if you hadn't taken the game off the rails.
Much of the exploration in The Legend of Zelda: A Link to the Past is pre-scripted stuff like using a bomb on a cracked wall to open a hidden passage, but the world design still encourages rewarding exploration and self-discovery. Every time you get a new item, there's a world of possibilities for you to explore. Once you get the flippers, you can swim in water to find a wishing well behind a waterfall, or an extra bottle under a bridge. Once you get the Pegasus boots, you can start ramming into trees to knock out extra goodies. Once you get the magic mirror, you can warp back and forth between the light world and the dark world to reach previously inaccessible areas. Once you get the shovel, you can start digging up treasure virtually anywhere.
In the overworld map of Hyrule, there are dozens and dozens of hidden areas to discover, which not only provide you with tangible rewards (like heart piece containers or bottles or item upgrades), but there's also just a simple fascination of discovering that you can do creative things with the environment, like ramming into the lumberjacks' half-sawn tree, or pushing one of the gravestones back, or entering a hidden door in the backside of a tavern, or swimming into a cave behind a waterfall. These are the elements that made traditional Zelda games really fun -- having the freedom to make your own discoveries.
What bothers me about some of the more popular modern games is that the exploration is often extremely diluted. We're either hand-held so much that we never get the freedom to go off on our own, or we find randomized, level-scaled loot. The effect is usually that you just never find any kind of rewarding (or even interesting) content, and you don't get the opportunity to play the game in your own personal way, because the game is scripted to happen in an exact, precise way for every single player.
Rewarding exploration and self-discovery is of course not essential for every game, but it plays a very important role in free-roaming RPGs, and can be potent enough to turn mediocre gameplay into an engaging experience.