A strong contender for my favorite game of all time. Everything I loved about Fallout 3 is still here, sometimes improved, and the new base building mode is really fun (although the interface could be better) and gives all that worthless junk you could loot in earlier games a real use. The real time combat feels a lot better in this one, the shooting mechanics are much smoother, at last on par with what you expect from a modern first person shooter, and you can even modify your weapons (another new incentive to loot as much as you can). The map is huge and the wasteland looks amazing, especially the lighting, and is filled with interesting places to explore and quests to do. The only thing I don't really like is how the dialogue UI has been simplified, the text descriptions for the possible answers are so short that, sometimes, you aren't sure what they really imply... Apart from that, it has been an amazing experience so far (I just finished the main story, after playing for more than 65 hours, but I plan on exploring the wasteland some more).
More info: https://en.wikipedia.org/wiki/Fallout_4