A summary of Fallout through the ages:

Fallout 1 and 2: Top-down isometric RPGs set in a postapocalyptic retrofuturistic America. The sequel is a direct continuation of the first game (you are the son/daughter of your character in FO1) and is even more well received than the first. Both are well received by critics and gamers alike. The stories for both center around fighting for your people (your Vault in Fallout 1, your kidnapped village in Fallout 2) and the endgame is objectively good. However, both games give you the option to be evil and side with the villain, completely changing the ending. Both games also had several ending factors and your impact on settlements and people groups are told to you through a slideshow. The entire ending could be changed just by picking a perk (look up the Bloody Mess ending).

Fallout 3: Bethesda buys the rights to the Fallout series from Interplay and gets to work making their spin on the series. That's a HUGE oversimplification of what really happened, but it works for this. Fans and critics were eager to see how Bethesda, riding on the acclaimed Elder Scrolls series, would tackle the classic RPG series. Fallout 3 releases with a bonkers story and first-person gameplay but manages to retain mechanics from the classic RPGs to keep old-school fans happy. These mechanics include, but are not limited to: Unique items, skills, perks, and karma. Fallout 3 receives critical acclaim. The plot itself is a mishmash of the Fallout 1 and 2 plot but nonetheless feels like Fallout. There are only two possible endings (later retconned with DLC, predating Mass Effect 3's blunder) and the slideshow is hugely oversimplified.

Fallout: New Vegas: Developed by Obsidian, a company full of the original devs from Fallout 1 and 2, and made in just 18 months in the Fallout 3 engine. New Vegas releases to "okay" critical reception, critics citing bugs and a general lack of polish as downsides, but praising improved shooting mechanics and a much better story. New Vegas keeps skills and perks and adds traits, along with reputation and an improved, more weighty karma system. The game is frequently cited by many as the "best" Fallout game due to its superior story and accessibility to new players. The game's four DLC packs also tell one coherent story that adds depth to the player character's background and show other locations in the Fallout world, such as Utah. Like the old Fallouts, New Vegas has many ending factors and a main plot that doesn't require an emotional connection to anyone or anything. Any character, regardless of importance to the plot, can be killed, and the game's main quest still continues. An entire DLC can be skipped by killing one NPC (Honest Hearts, look up Chaos in Zion). The game's final boss can be bypassed with Speech and Barter checks up to 100, making many skills useful. It is also possible to use your skills to bypass entire sections of quests. Many side quests also have branching paths in themselves, certain endings rewarding you reputation with certain groups, good/bad karma, and rewards. Due to the short development time, Obsidian's vision could never be fully realized, which is evident by the Legion, an idea left over from a cancelled Fallout game that couldn't be fleshed out due to time constraints.

Fallout 4: Bethesda's shot at a Fallout sequel manages to improve on the beauty of the world, crafting, and shooting, but a lack of focus on story and player mechanics create a muddled mess of a Fallout game. Skills and traits are gone, everything is now decided through perks. Any skill checks are replaced with Charisma checks, meaning you can persuade an NPC more easily the higher your Charisma stat is, but it is still a dice roll, i.e. you have no guaranteed success, unlike skill checks in Fallout 1-New Vegas. The plot tries to make you focus on losing a wife/husband and child you have no connection to and generally has no open-ended gameplay. All quests end one way, and the game can end one of two ways. The war on synths has no relevance to your character, since every Fallout protagonist before the Sole Survivor has been invested in the main conflict since it affected the world they lived in. The SS is a man out of time and has no connection to the Commonwealth. Fallout 4 also misses the potential of moral games with the synths, asking the question of "what makes a person a person." Far Harbor does this beautifully. Bethesda also added the settlement building mechanic, and given the amount of DLC for it, it's obvious that it was their focus. Hardcore fans felt betrayed, as the season pass now gets them a bunch of DLC for a section of the game they likely won't use and was advertised as "completely optional."

Fallout 4 is, in no way, a bad game. It's a right awful Fallout game, but it's not a bad game on its own.