(Do forgive me if this sounds more like a review. Mostly Spoiler free; you're good if you've gotten half-way through the main quest.)
First up, stuff which is either nitpicky or good:
Once I got up to level 25, enemies just stopped mattering. I've got almost 200 stimpaks, and I'm worried I just might cause an integer overflow with all the (Useless .38) ammo I have. I'm assuming this is just because I'm doing tons of sidequests, some of which I got in the early game, so I can't expect those to be challenging to anyone above level 10 or so. Not that rampaging around a raider-filled store isn't fun, mind you, it just gets old after a while.
One thing I dislike about the new gameplay is the fact that useless ammo is really common, while stuff that I actually need is incredibly rare. Sometimes justified, sometimes not, but either way it would have been nice to craft your own. It has allowed me to roleplay as an Ork, though, using pipe weapons, so that's good, I guess. Just never aim down the sights, and make sure to use a drum mag. It's really fun, trust me.
I love the new cast of companions, as well as the factions. The Institute enemies are quite fun, seeing as how I'm essentially hacking apart T-600 Terminators with a machete. Gunners are fun, but I think we've all seen enough 'generic evil mercs' to last us a while. The Minutemen are quite likable in that they provide amazing contrast to the Enclave. One represents evil, pre-war America, the other shows us what America could have been without the evil and corruption. I have mixed feelings about the Brotherhood of Steel, but they've given me a metric ton of fanfic fuel.
The companions I've unlocked so far are all unique, but seem to share a common theme (except for Dogmeat). Not sharing what it is, for the sake of spoilers, but it's easy to figure out after a while. I loved Blade Runner, so nick Valentine is who I've stuck with for quite a while, but I'm planning on using Curie once I've done Valentine's quest. Not sure what her carry limit is, but I hope it's really high.
I also love the new crafting system, especially it's reverence of dakka. It's like Skyrim and New Vegas had a baby, which was then raised by Orks. By that, I mean you can add an automatic receiver to almost anything, which is awesome. You can also make drugs out of antifreeze and detergent, which is funny in it's own way. The crafting system, while quirky, is most certainly the best seen so far.
Now for the bad:
Glitches galore. I had a Deathclaw rush me a while back, and I accidentally backed off a cliff. The Deathclaw followed... but wound up simply running off the edge and into the air like a Loony Toons character. While funny, it does show me that Bethesda really doesn't seem to think very highly of quality control. This isn't the only noticeable glitch I've seen, either. During a firefight, Nick Valentine's dismissal menu popped up for no reason whatsoever, so I tabbed out, thinking it was just a small glitch. But, then he decides to dismiss himself back to the Red Rocket Truck Stop, and for some reason, his disposition dropped like a ton of bricks on Jupiter. Fortunately, I had an earlier save, plus the Debug Console, but this is getting ridiculous.
The performance is not nearly as good as I'd expect, either. Mad Max had graphics that were about on-par with Fallout 4's, and my computer, for all it's faults, is quite powerful. So, imagine my surprise when I can't even get a steady 40-FPS on 'ultra' settings. And this is after digging through the game's files and optimizing everything I could. Even with some of the settings on high, I still get >20 in some areas, none of which have obvious sources of performance loss. I'm talking about getting 60 FPS looking at the glorious HD world from the top of a city shop, but a five-foot patch of nondescript dirt lowers my performance down to twenty.
Finally, I feel that the new radiation system does not work very well at all. If they were trying to be more realistic, it isn't, and I'm not entirely sure why they'd want it to be more realistic, given that Fallout runs on pure SCIENCE! It's really quite annoying to run little damage calculations in your head now, because every rad you take makes you need to recalculate everything, as opposed to every level of radiation sickness or so. And that's without getting into contaminated food. I can't tell you how much food I've wasted simply because radiation deals percent-based damage, while food heals a fixed number. For me at least, this new system takes a lot out of the game, due to rendering found food items nearly useless to me.
And now, we tackle the ugly:
Power armour. Almost everything about it, this time around. While I like the return to the 'walking tank' portrayal it originally had, the almost-certainly game balance induced need for fusion cores sucks. There, I said it. It sucks. I have never before needed a glorified battery to run my power armour, so why now? This is a world where forearm-mounted computers can run for 200 years on an internal nuclear power source, and now you're telling me that I can't even get a day's worth of charge out of my armour? How did they manage to effectively deploy it during Anchorage? More importantly, how does the BOS manage to not run through their entire supply in one day? I can handle reasonable, well-used retcons, but this just breaks canon in so many ways. They should have gone with a Powered Power Armour-like system (It's an awesome mod for New Vegas). I fought a legendary raider wearing X-01 armour. Didn't even need a stimpak. So, no, game balance is no excuse for nerfing something in this manner, given how broken the game balance already is, and especially given just how many other ways exist to balance the armour.
Ultimately, I give it a 6 on a scale of one-to-ten, for being fun while also being glitchy as hell, having non-existent game balance, breaking its own canon, and using the English language. I think we need to wait a while for some patches before I truly write a review, though. Also, if it seems like I complain a lot or just savaged the game, that's pretty much normal for me.