Ok this is one of my all time favorite games.
Oblivion is a role-playing adventure game and uses open-ended or Sandbox gameplay. The main quest can be postponed or completely ignored as the player explores the expansive game world, following side-quests, interacting with NPCs, and developing their character. Players are free to go anywhere inside the province of Cyrodiil at any time while playing the game, and even after completing the main quest storyline. The game never ends, and players are able to build up their character as much as they want, with no restrictions on skills or equipment. The Windows version of the game is open to almost unrestricted modification, and there are thousands of modifications available on the Internet. These modifications vary from minor item changes to complete game overhauls. The game provides a wide variety of enemies, including monsters and animals. Enemies become stronger and weapons become more powerful as the player's character becomes more proficient in skills. This game mechanic, called "leveling," keeps the difficulty constant throughout the course of the game. The player, however, has the option of adjusting the difficulty level.
The fast-travel system found in Arena and Daggerfall made a return in Oblivion. In Oblivion, when players visit a location, that location appears as an icon on their map. Players can then return to this location instantly. The in-game time is adjusted to reflect the time that would have elapsed were the player to have travelled there manually. One major focus during Oblivion's development was rebalancing Morrowind's stealth and combat skill sets. The skill system is similar to Morrowind's, though in Oblivion there are fewer skills. The "medium armor," "unarmored," and "spear" skills are removed altogether. The "short" and "long blade" skills are condensed into a single "blade" skill, and the "axe" skill merged with the "blunt" skill. The ability to "forget" spells was also removed. The game also introduced "mastery levels" which give skill-specific bonuses when the player reaches predetermined levels in a skill. The combat system was also revamped, with the addition of "power attacks" (added upon reaching specific mastery levels), and the removal of the separate styles of melee attacks present in Morrowind. Ranged attacks were also changed so that hits were based on the player's firing skill rather than the character's numerical skill level. Spears, throwing weapons, and crossbows were removed. The choice came from a desire to focus all development effort regarding ranged weapons into bows specifically in order to "get the feel of [ranged weapons] as close to perfect as possible" as the Havok physics engine allowed the team to do. Morrowind's passive Block skill became an active feature in Oblivion, activated by a button press. The dynamics of the blocking mechanism were also changed, causing enemies to recoil after a successful block and leaving them open for a follow-up attack by the player. Most of these changes to combat were received well: GameSpot commended the strengths of the game in each area, finding the game's melee combat "faster and smoother" than Morrowind's, the game's stealth combat "at least as satisfying" as its melee combat, and was generally impressed at the breadth and ease of use of the game's spell-casting.