People are going to hate on any and everything that receives attention - especially on Metacritic. Even The Witcher 3, which had its flaws for sure (imo), received a lot of unfair heat (mostly before it released, the whole graphics downgrade thing everyone was talking about).
Metacritic is awful. Plain awful. It's ratings have little to no value. The critic rating was revealed to have different sites/reviewers carrying varying weight on the overall rating (so an 8.0 from IGN will impact overall rating more than an 8.0 from a lesser known reviewer), and if you believe in the idea of paid reviews, you can see the flaw there. User reviews are just... the worst. Either flooded with 10/10's or, in many cases, bombed with 0/10's using multiple accounts. The entire site is a joke. Thankfully Steam got rid of the "sort by Metacritic rating" option, and hopefully will remove the Metacritic score found on each game's store page as well.
As far as Fallout 4 goes, I have absolutely loved it from release. I've been playing it when I can since then and have about ~80-90 hours on it. I'm level 40 and still easily have half the game+ to do - quests, areas to explore, etc. Modded it a decent bit, including the Create Your Own Difficulty Rebalance mod with these settings: Enemy Damage +150% (Survival default is +100%) and Player Damage -25% (Survival default is -50% which makes enemies a bit too spongy) + a mod that scales all enemies to your level and beyond so they're a lot tougher and have gear that matches their level + Arbitration which improves Enemy AI (I'm using the Enemy AI, Lowered Weapons, Radar Reduction, Fall Damage, Increased Grenade Detection, Molotovs Burn, No Auto-Regen for Limbs, and Reduced Grenade Spam modules).
All of those and some other mods + a few rules I set for myself (No fast travel except to/from major hubs or settlements, carrying limited ammo, limited chems/stimpaks/etc.) have made the experience x10 more enjoyable and immersive. The wasteland is now an even more cruel and punishing place. I have to use my ammo wisely, plan my routes for cover and resupplying, set up ambushes with explosives before aggro'ing groups of enemies, running away when it gets too tough, etc. The limited Fast Travel has allowed me to experience so much more of the wasteland I never would have had I just teleported everywhere I needed to go. There's so many random events you miss out on when you do, and the game feels empty and far less impressive when you aren't travelling on foot everywhere. I've thoroughly enjoyed the game thusfar, and expect to continue to do so.
I've always been a huge Fallout fan, so I understand not everyone will feel this way. Some people who weren't fans or hadn't heard of the series before Fallout 4 may have gotten caught up in all the hype generated by the fans and came away a little disappointed, but others may have ended up liking it more than some fans of the series because they didn't have the previous ones to constantly compare it to. It's a dangerous thing being a big fan of a series. You love the early games so much that you can become incredibly critical of new games in the series. You're constantly comparing it to how you felt when you played the others or the first game that you never stop to truly take in and enjoy the new one you're actually playing. And oftentimes those previous experiences are warped by the sense of nostalgia, and the games themselves weren't really as great as you remember.
Yes, this game has its flaws, no doubt. The RPG element has been dumbed down a bit, though some of which I understand their reasoning for doing so.
The skill points (ie. Medicine, Heavy Weapons, Science, etc.) have essentially been merged with the old Perks system to form the SPECIAL stat Skill Tree. Instead of putting points into Heavy Weapons, you now grab the Perk in the Strength tree that increases damage when using Heavy Weapons. Rather than putting points into Medicine, you grab the Perk in Intelligence that grants a boost to the effects of Stimpaks and Rad-Away, and etc.
The Karma system, while fun to look at and have, was never really that great or very thought out to begin with, and could sometimes screw you over on things. Personally, I'm fine with this not being in the game anymore.
The change to dialogue-checks is the only real one I'm disappointed in. I thought they gave more depth to your character and helped to really define the type of character you had. The dialogue changes in general I don't really mind since Full Dialogue Interface came out, allowing the entire lines of dialogue to be shown on the selection list.
The lack of friendly encounters is another thing I've found lacking. Everything seems to want to kill you, it's rare to come across anyone or anything (save for the random trader/Caravan) that's not automatically hostile from the start.
Anyway, I'm sure I've rambled on for far too long here. My point is, the game - for me - is great. I absolutely love it, and will continue to for quite some time. With some neat-sounding DLCs coming in the future (especially that huge one with Maine) and the CK / Mod Tools releasing soon + the new Survival Mode that'll require you to Eat/Drink/Stay warm/Stay healthy/etc., I'm looking forward to playing it a lot more. I recently decided to take a small break from it after hearing about the Survival Mode changes coming out so I don't get too burned out on it yet (been playing some XCOM 2 and Dying Light - The Following instead) I understand that not everyone is going to enjoy the game as much as I do, but I think some people are too harsh on it as well, and are preventing themselves from enjoying a fun experience. The game has its flaws, every game in the series does. Every game in general does. No game will ever live up to each and every individual person's expectations on how it should have been. So instead of us constantly trying to compare a game to how we thought it should be or against the previous games in the series, let's try and take the time to enjoy the game at hand.