Sid, its aims are whatever you want really.
Be nice, be a thief, be a bastard.
You can play for hours and hours without even touching the main questline.
Building up money, buying houses, even getting married if you really want, and of course adventuring in whatever style you want, sneaky, magic or just a fuck off big sword.
Finally got around to modding and putting hi res textures in, mmmmmmmmm