Morrowind: Oblivion, predecessor to Morrowind: The Elder Scrolls 3. Both amazing games.

Unfortunatly only single player, a hugely huge world based in a fantasy land Tamirel (i think Vvanderfell was in tes3)
You can pick your race of imperial, nord, and summit else human, dark elf, high elf, wood elf, orc, and wierd fish thing 'aragornian' Each have advantages and disadvantages.

The game has 3 main choices however is COMPLETELY open ended, based mainly on strength (sword/mace/axe fighting skillz) Stealth, (sneaking, lock picking, picking pockets) and magic with mages spells, got the school of destruction, illusion, mystisicm, alteration, and cunjouration. Theres hundreds of spells in the game, you are able to work to be allowed to uset the mages alter and create your own spells!

The skills system in leveling up your fourty odd skills is quite complex, i made my own character, so i was able to select my own major skills, every 10 majour skills you increase you 'level up' however depending on what skills you increased in each level adds a mulitplyer to attributes which are govorning the skills, there are 9 of these so all the skills have a governing attribute.

There are an endless amount of quests, i find however the game lacks humour. yes, humour. Theres an even bigger population, guilds to join, monsters and evil to kill, bandits to be sleign, the arena to be stained in your bloody fights, bets to be placced, houses to rob, dungeons to loot, MORE dungeons to loot, EVEN MORE etc

The graphics are beautiful, and can be notched up v high, and looks fab, i downlodaed some graphics packs to change parts of the game and a 3d sound overhaul too..

i aint really said much about the game, its ace you should all at least try it.

The game is completely moddable, there are a few good sites that host loads of mods, tesnexus
mods just download as one file, sometimes bigger ones come with textures and meshes you just copy em over tick the box and they work.. most of the time check feedback etc
loads of feeback and is i dare say the biggest bloody amount of people playing a single player game EVER.

Honest i could write a proper two pager and it would be hard to squeez in even half of whats in the game, whats cool about it, whats ace about it, whats bloody awsome about it! buuuuuuut its single player..

plop.