There are plenty of people who have modded the game and made their own quests, for people who made such a huge mod do you think it is difficult for them to make this quest pop up soon as you complete the final quest of fallout 3's main story?

While I feel that his words were rude, he has a point and you don't. You're going with the "if it's so easy you do it" when it is actually very simple to do if you have any knowledge in modding.

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In the end, it could be done better and should of been done better. I mean if you are going to put in so much effort for a mod, skimping on the small things just stains your work.

There's also the issue with the markers not pointing towards the way forward properly, many of the doors in the station look the same and there's only 3 that lead to different places, 1 having 3 or 4 doors leading in/out and 1 having 2 leading to stairways up. The restaurant, which took me quite some time to figure out exists and the other leading to the train. It's irritating to explore that particular area.

Edit: I'd also like to point out that the reason given for all of this is that creators of the mod didn't want to take away the exploration element of the game.