This is one I posted a while back, it's fairly applicable to this thread so I'm just going to copy paste it, it's long but I'm pretty confident that it correctly conveys my thoughts on the matter :)

"I might be a massive outlier here but I don't think Fallout 4's modding system was good. I do't even think it was an improvement on New Vegas' modding system in some aspects. In New Vegas you got a gun, you liked the gun, you wish the gun could kill people better. a few levels go by and your gun starts under preforming. You are sad, you stop using gun. Suddenly, you find a merchant that happens to have a mod for your gun that makes it better than viable and can even change the way you play with the weapon, you have your favorite weapon back! But you don't have enough caps for it, mods are an expensive commodity in the post apocalyptic world. You have to sell some useful stuff as a trade off or collect some bounties to earn your new weapon upgrade, you EARN your improved weapon, it comes with a sense of accomplishment and achievement, and nothing beats the excitement of finally stumbling across a good mod for a weapon you love in New Vegas.

Contrast this with the mod crafting system in Fallout 4. Sure, it's a neat idea in a brainstorming session in Bethesda Softworks; 'What if we let players find components out in the wasteland that they can use to make mods?!' but I don't feel that it translates into anything but an annoying, time wasting, grindesque game mechanic. It turns the game into a 'Pick random shit up and horde it' Simulator. I've always had trouble in Bethesda games with inventory management, and adding the fact that I now have to actually pick up all this random shit from all over the place just makes it even more annoying. And that's another point. This shit is EVERYWHERE. You can pop down to the nearest landfill and find the same components necessary to build either a long barrel for a 10mm or a goddanm MIRV launcher for a Fat Man. There is no challenge in finding the stuff needed to make weapon mods, other than the fact that you can never get enough adhesive, but that doesn't add challenge, it just adds frustration and annoyance. Whats more, if you're in a pinch it's only a matter of fast travelling to 5 or 6 different merchants to find all the junk you need to create whatever mod for whatever gun you want. And the junk costs about as much as a four day old dog turd in a can. There is no CHALLENGE present in the Fallout 4 modding system. I have never had a feeling of, 'Yeah, I've worked hard for this mod and it's really changed my gun for the better' when playing Fallout 4. Only feelings of frustration that I don't have enough metal spoons to give my .44 Magnum a better handgrip to give its stats a .05 boost to accuracy.

That's another thing, the potential mods are so saturated that upgrading in the normal progression doesn't feel like you've done anything because the stat boosts have to be balanced between all the potential mods. When I put a better receiver on my gun in New Vegas I got a decent stat boost, +30% or +20%, it was noticeable. In 4 I get a +5% tops, it's only noticeable if you're upgrading at a high level, and by then you've managed to horde so much random shit that crafting is about as difficult as hitting water after you fall out of a boat. Which brings me onto my final point.

The level gating. In my last two playthroughs I've managed to collect the sum total of about 600 tonnes of scrap while waiting to level up enough to unlock the last teir of 'Gun Nut' and 'Science!' I had all my weapon mods maxed out for about 6 or 7 levels, I had spare perk points, the only thing stopping me from upgrading my weapons more was the goddanm level gate on the perks. So I saved junk to use when I finally got there. By the time I leveled up enough I had enough junk in my trunk to fully upgrade every single weapon in my inventory in one go. How did I feel afterward? After all that time spent, I finally had all my guns fully upgraded. I felt empty, I felt bored, I felt like all that time spent looking for components was completely wasted. 'Oh, my gun is a new colour now, the mag is slightly bigger than before and it does 7% more damage... yay...' I didn't feel like I had earned those weapon upgrades. They all went on as soon as I got to level whateverthefuckitis. This, coupled with the complete lack of weapon variety in 4 made me lose all interest in the game, I was bored of the weapons.

In conclusion, I think Bethesda should have gone with a 'less is more' approach to weapon mods, making them more impactful and useful in the game, as well as more rare and valuable. The acutal mechanics of weapon modding are cool, I'll admit that, and a LOT more streamlined and polished than New Veagas', but it's let down by so many other aspects of the game, the level gating, the lack of weapon variety, the over saturation of weapon mods. It was good, a step in a possible right direction, but it is my opinion that it needs a LOT of work to be fun and enjoyable.

Hate me, shout at me, call me a fanboy. This is my opinion if you don't like it, too bad. I'm in the same boat as you, I bought Fallout 4 under false pretenses too, I find it difficult to be this damming of a game I've put countless hours and €60 into, but I have to be honest with myself. These are not rose tinted glasses, I played another game of New Vegas after 4 and I enjoyed it so much more. If you've read this far congrats, I'll buy you a muffin."