An honest review form an honest player.
Basic summary of the beginning.
You start by finding yourself in prison when you first meet Emperor Uriel Septim, who claims to have seen you in his dreams. after a brief spell with the Emperor you are set about your adventure.
During the course of the game you will meet many characters such as Kajiit, Nords, Argonians, Redguards, Elves (High, Dark and Wood Elves), even the Emperor's illegitimate son, all of which will at some point prove to be useful to you.
Oblivion lets you create a character specifically to your own tastes whether you like an all out meat sack warrior type, sneaky thief type or your magical type you can create which ever you want, you can even mix attributes to create your own custom class character, male or female (Lizard, Cat and Orc too.)
Once you have decided on your character you will inevitably join a faction or guild. The guilds are: Fighter's, Mage's and Thieves. The factions being: The Dark Brotherhood, The Blades, Arena, Knights of The Nine(Plug-in needed), Knights of The Thorn, The Order of The Virtuous Blood and Mythic Dawn (only joinable Temporarily) all with their own set of missions for you as you rise in the ranks.
The Empire of Cyrodiil spreads across vast countryside with the obvious features such as mountains, rivers, lakes, cities, farmland, and much much more, you even get the chance to explore the realm of Oblivion itself. You will soon discover while playing the game that its no small feat to explore the entire map (Which conveniently comes with the game disc).
There are countless caves, dungeons and Aleyid ruins to find, explore and most importantly loot, some holding treasures unattainable anywhere else. These could me anything from rare weapons and armour to valuable gems for bartering with, so theres always a reason to keep moving around the wild. Dotted across the countryside there are also wayshrines to The Nine Divines as well as Daedric Lords. These will either allow you to receive blessings at various chapels in the cities, grant you temporary use of special Daedric weapons and armour or even side missions for the Daedric Lords themselves.
If and when you do complete everything Oblivion has to offer you may realise that you have spent far more time than you had originally meant to playing as its hard to put down once you get started.