Fallout 4 is an excellent and fun game. If you liked Fallout 3, you will certainly like this one. But that's also the game's biggest shortcoming: it's almost exactly like its predecessor. Just like F3, you start in a vault. Like F3, you escape and you look for someone. Otherwise, it's the same game, with the same positives and same failures and limitations.
The developer's idea of mixing it is that this time you escape the vault to look for your son, whereas in Fallout 3, you escape the vault to look for your father! There were some minor improvements. For instance, the graphics are better (though still far behind other AAA games) and the shooting has been improved. On the other hand, some things took a step back, including the dialogue options and the leveling system. The dialogue, as others have already criticized is too limited and lacks creativity. As for the leveling system, well my problem with it is that I finished all the side quests, did a fair bit of exploration, and finished the entire main quest, and I was still only at level 37, which means I wasn't leveled up enough to unlock some of the game's most important "perks" (skills), some of which require level 50.
The point is that the game encourages grinding. It wants you to spend a lot of time building settlements (which I don't care to do), and doing some quests for the different factions that literally never end and are very repetitive. That's basically how it expects you to reach higher levels. I wish they'd kept the system implemented in Fallout: New Vegas (which is a game I actually prefer).
I enjoyed Fallout 4. But I wish it were a bit different. I want less grinding and more role-playing. And I would like better quests. The quests found here are mostly vanilla kill/fetch quests. I'd like to see more interesting stories, more mature themes (care to try something edgy, for example?), and more creativity in how quests are solved. This is just more of the same, and that's not exciting anymore.