HOW BIG IS THIS GAME?!

I have been playing for months and Ive been doing so many of the quests but each time I finish something I have 5 more new things to do. I dont even know what the main quest is! At this point my character is some kind of stealthy two handed tank mage, and surprisingly good lockpicker. This game is so freaking massive and I am finding new things all the time. Ive barely started any of the DLCs, but I want to know at what point are you close to finishing the game