Graphics:
I dont think people realize just how much is rendered in a Bethesda universe, but i'd think it'd be fair to speculate that they put more objects (especially ones that you can manipulate) into their world than any other game out there. So when you compare the 'open world' graphics of a game like Witcher 3 to Fallout 4 a better comparison might be to focus on the artistic look and feel and not directly compare frame rates or load screens (or lack thereof); and also you have to realize there's always trade off with these things because of physical memory limitations; maybe a simple example would be objects (polygons) vs high quality textures
Load screens:
I've been playing Bethesda games since Morrowind, this game has less load screens (transitions) than any other Bethesda game in the past and for me and most other people i see not having configuration issues or hardware limitations seem to be having almost negligible load times of 10 seconds give or take
Content:
this game has hundreds of hours of content (whether you like the content or not); it would take too long to list, and others have already done it in other threads; to me this is the most moot argument
Replayability:
I think the new perk tree combined with the removal of the lvl cap greatly increases replayability allowing you to take many approaches to your wasteland experience; put simply you need to reach lvl 270 to have max special with all the perks; so i guess you can become God, but it'll probably take you as long as it took him xD; I also really like the new perk system because i really dont like the mountains of numbers that a lot of rpg's use, its one thing to work with some stats here and there but a lot of RPGs end up turning into a physics exam where you need a formula sheet and i think this just absolutely takes away from immersion and any kind of realism
Combat Mechanics:
I've seen a lot of people (including myself) point out how much better the real time combat mechanics are; the new grenade key implementation has some complaints, but as pointed out this is due to the limitation of console controllers and I think we can all agree its still better than having no grenade key at all; there are plenty of us that use the grenades without any problem
Dialogue:
This is an area i think the general consensus is that there's plenty of room for improvement. I do like the new mechanic of how conversations are handled, but the lack of options and outcomes is certainly noteworthy; i really do hope mods can help out in this area if possible
Atmosphere:
I feel that this Fallout is definitely more immersive and fun to explore than the previous ones. I feel like there's a lot more going on, more to find, and with the new weather system and lighting I feel a constant shroud of suspense as i roam the wasteland with action around every corner keeping me on my toes
Stability:
I've seen quite a few posts (again, including my own) from people that have played many of the previous Bethesda games and I can definitely say that this one is by far the most stable on release. Bethesda games always have bugs and crashes because the scope of their games are HUGE, but i can run this program on my laptop for literally days without any issues whatsoever, and i certainly couldn't do that with the previous FO and ES games. Shoot if you even alt-tab out of FONV (w/out mod) it crashes the game.
I could probably add a lot more, but I feel like most complaints i see are all about what the game doesn't have and skipping over all the things that it does have. Also there is so much subjective comparison to other games and people complaining because Bethesda did not design the game around their own personal preferences or gameplay strategy.
I feel like people's expectations for this game were unrealistic so many felt let down, but i think more focus should be put on what is there rather what isn't; glass half full point of view
fact of the matter is for 2015, and by comparison in the marketplace, this is a phenomenal game that will pull you in and keep you busy for days
i could add more areas to critique like settlements and crafting etc. but i've typed enough now so i'll leave that to you
