Show don't Tell is a great rule for writing, and it IS a rule a writer should consider when making a game, but, if you are creating a RPG game world from scratch, the history, lore, etc(which FO is), then you do need a mixture of both Show and Tell. Mainly, because games are limited, where as when writing a book, one is not. If say they showed everything talked about in NV, the game would become the impossible game, would have never been made, because of too high a goal. Show the first battle of hoover dam. Show the BoS vs NCR war. Show the battle of Helios. Show the Powder Gangers escaping the prison. Show Bitter Springs. Show the political corruption of the NCR back in California. It becomes an impossible task to do all this, so what they tell you, is the past. Nothing wrong with that at all. In a book, you can do that via flashbacks, or just start a book in the past, but unless your story is going to begin at the dawn of time, there will always be some past that either needs some telling in some fashion.
In the older style of games, some of what was told instead of shown, could have been possible, because the map node system and a much larger game world. The style FO games are now in, your story is going to be limited by the playable area, so something will thus be impossible to show, and must be told.
BGS didn't do a great job of telling in FO 3. There are a lot of questions of how things appear or happened that the game doesn't go into, that people have debated in lore for a long time, because the game, in certain aspects, is vague.
The other thing they did not do well was proper choice and consequence. Not every decision HAS to have C&C, but some things in FO 3 became ridiculous, blowing up Megaton one of them and the utter lack of any consequence in doing so. Being a slaver, not much consequence. You are still welcome into every settlement regardless, you can commit murder and be welcomed back. NPCs do not react in realistic fashion to someone who does these things. Part of the problem is that there was no proper way to complete the game as an "evil" character, and an "Evil" character was forced to go down the same "good" path, but given two stupid "evil" options that really don't make any sense, and are only useful if the evil character you are playing is an utter psychopath, with no regard for anyone else or even themselves, and then the question is why in the wide world of sports would people like the BoS and what not be sending the known most evil person ever out to do important stuff?
Also, consequences don't always have to be horrible. They can be subtle, opening up or closing other options down the line, or potential dangers down the line. They don't have to doom anyone, although sometimes a consequence will.