It is a very well-made recreation and remix of the first two Fallouts, with some very minor mechanical changes, otherwise, just a really interesting setting. One of the things it does differently is that it makes the non-combat skills rather useful - you get XP from going through dialogue, so having high INT and Speech is rewarded that way - you can also apply Science to things for XP as well as Repair things which also results in XP, as well as sometimes results in items.