I'd like to see in Fallout 4:
* A real main quest, with a real and well written scenario without too much plotholes and a bit more involving.
* More background content, pre-war recordings...
* A music more in line with the Fallout tone. The music in Fallout 3 is sometimes adapted some other time it just feels out of touch or more adapted in an Oblivion. Some tunes actually reminded me Oblivion and, well, that's not a good thing since the ambiance is quite different.
* A more balanced ruleset. Either keep the ES one with its fluid automated skill and levelling abilities either just take the SPECIAL as it was in Fallout 1 or 2, but please, don't try to painfully shoe-horn the SPECIAL into this unbalanced mess. One should not be able to have such versatile characters so quickly and so easily.
* Some new factions, if we are to be on the east coast, what's the point in translated all the western factions we've seen in Fallout 1 and 2
without adding anything new? This Institute from the Commonwealth should be a very good starting point and I'm pretty sure the FEV and Power Armours weren't the only projects of the US Army to get cheap, powerful and numerous troop.
* Better dialogues. I can count the very good lines on the fingers of my hand, while the rest is oscillating between bad to just okay. It has always been the weakest points of your games and I haven't see much significant changes here.
* A better interface. Seriously, it shouldn't be a subject of complain but what in hell is so hard to add some shortcuts like "I" to go directly to the inventory, "M" for the map, "C" for the character screen...?
* If you are to stick with the forced gore system, it'll be great to add more animations when we are killing enemies so we don't see the same one each time. But being able to opt-out the system and just quickly seeing the result without a slow-motion passage is a must-have.
* We have the open-ended universe, a big wasteland to explore, quests with many possibilities to end them, so why on Earth does the main quest deny me the possibility to actually chose how I'll end the game? I mean, given the circumstances,
Spoiler there are a lot of characters immune to radiations who could have done this, robots, super-mutants,... and no possibility to convince them to do it since they won't risk anything more than our eternal gratitude
.
* A real enhancement in the writing in general. This has always been the weak points of Bethesda game and I'd really hates to see that they don't acknowledge this and work hard to change it. Once I'll have the current strengths of Bethesda game plus good dialogues, NPC and main plot, I can't really see what could be said against such game.
* A better polishing. There is still a lot of bugs in the quests and I can't see how they could have not been fixed during QA tests since they're well-known and, well, missing robots in Big Town are hardly something which we cannot see...