How much else to do in Fallout 3 after finishing main quest..*Possible spoilers*

Hey, let me first say that I have loved playing this game so far. I ventured off into a few side quests, but I mainly concentrated on the main one and completed it in about 20 hours. I'm the sort of person that plays games but never finishes them, but I really liked this game and did it in 3 days. I have a few saves before the end of 'Project Purity' and am going to venture back out into the wastelands to find other side quests. Is there a lot of extra content for me to do? I don't have access to my pc at the moment, think im up to to level 12...so it still seems like there is more things to do.

Yeah I just mean random quests, such as the ant quest etc.. Is there much else to do other the main project purity one?akust0m

Do as much as you can, you can't continue after beating the game.

But if you have a save just before it finishes, could you just load the save, leave that area and go do other stuff?akust0m

The point of no return is when you go with The Brotherhood on that final assault. 

Hmmmm...my saves might be after I accepted that quest. akust0m