For newcomers to the world of Fallout, 4 is a great place to start. Developed by Bethesda (The Elder Scrolls series), the Fallout games are action RPGs set many years after the world has been ravaged by nuclear war. The stories in the games aren't connected, but the themes and settings are all very similar.
In 4, you'll be traversing a post-apocalyptic version of Boston filled to the brim with robots, mutants, mercenaries, and raiders (some dangerous, others not) as you attempt to find out who murdered your wife and kidnapped your son. They payoff isn't great, but as with all Bethesda games, the experience is not about the destination, but the journey itself.
Unlike previous entries in the series, which featured drab color schemes and arguably depressing environments (it is a post-apocalyptic world, after all), this version of Boston is filled with vibrant colors and beautiful landscapes. It's a welcome change, and you really feel like you're actually discovering new areas as you explore, unlike Fallout 3, where everything looked the same. You'll even be able to build your own base in 4, though the mechanic is really just an unsatisfying distraction.
Anyway, while the environments have gotten more complicated, the gameplay has become more simplified. Weapon degradation is gone (thankfully) and the skill system is much more straightforward, which might turn off gamers who love constant stat checking and the min/maxing that goes along with it. There are a nice variety of skills and weapons to play with, though, so it's still a lot of fun- and almost always viable- to personalize your character to suit your preferred play style.
Dialogue is simplified, too. You converse with other characters via a Mass Effect style system in which you are given four basic responses to choose from and then your character says a drawn-out version of your selection. Unlike Mass Effect, though, in Fallout 4 my character usually ends up saying what I meant for him to say, and the conversations (as always) are as intriguing as the combat.
At the core of Fallout's combat is the VATS system, which makes the gunplay very unique when compared with other shooters. When you activate the system, time slows down and you select a part of the enemy's body you would like to shoot (with on-screen percentages telling you your chances of success), and then pull the trigger. This makes for some tense clutch moments when you're almost out of health and fighting a fast-moving enemy, and it's never not satisfying to watch a slow motion headshot land right on target.
However, there may be times when you have a 100% chance for that headshot and then the enemy suddenly glitches 30 feet into the air and you miss completely. Bethesda games are known for their constant glitches and bugs, which range from quirky to game-breaking in Fallout 4. One moment you may see cars cartwheeling through the sky, and the next you may try to open the in-game menu only to find that it's suddenly invisible and there is nothing you can do about it. Once again, the devs have focused on form over function, and while it works out most of the time, expect to get frustrated and totally pulled out of the experience more than once.
With all of that being said, the Fallout games are widely regarded as some of the best action RPGs ever, simply because of the fascinating atmosphere and setting, satisfying loot collection system, fun combat, and that addictive itch to always keep exploring and leveling up. If any of that sounds good to you, you'll enjoy your time with Fallout 4, but just keep in mind that it's not perfect... and while it isn't a step back for the series, it's not really a step forward either... it's more of just a step to the side.