1) More variety on attacks:
instead of just raiders and deathclaws it will be great to see other enemies from fallout aswell, such as mutants, feral ghouls(has chance to turn one of your dweller to a ghoul), slavers(if not prevented for too long will get lowest level dweller you own), enclave soldiers, cannibal cults, mad scientist with robots etc...
2)fallout caravan trader: Random times a trader will stand by in front of vault where in player can purchase items/equipments for a price and maybe only upto rare items, legendary/unique will still be exclusive for lunchbox.
3)More items: maybe adding some buff items will be good aswell eg: increase/faster production rate for 1hr, temporary electricity producer for 1hr, increase dweller(s) special(s) for 24hrs , etc etc...
4, 5 & 6 )More to build, sickness feature and Overseer Avatar:
how about adding rooms where it could increase dwellers happines status inside the room, also a room that will remove sickness and radiation of dwellers in a room
(so i think adding a feature where dwellers gets sick aswell is a good idea, some become ghouls some is constantly losing health over time some cant be happy unless sickness is cured some cant equip a weapon due to crippled arms, etc etc...),
i think it would also be great to have a room for defense where it will have turrets and be able to station dwellers in it only 2 dwellers on the vault entrance is very lacking, Barracks Room(dwellers in this room will automatically attack vault attackers inside the vault), and how about my own overseer room? And i think it will be good if players can create and design their own overseer avatar ?
7) PERKS: i cant believe there is no perks feature on this game
being fallout and all
As an overseer i think it will be good to see him have perks which is obtained the same way in fallout (through lvl up and some rare or unique ones are from books/magazine , and by achieving a goal/quest) and i think some dwellers should also have perks( unique dwellers ) eg: Preston harvey does 20% more dmg, etc etc
8) Shelter type: instead of just an underground bunker, give options to player if they want a fortress settlement or a bunker, it simply goes up instead of down and will have different images for the rooms.
9) Enhanced Exploration:
A feature where player can choose location to explore to, scavenge, and raid or attack, added to this feature, players can form a team of dwellers where it can be more successful, players can get food/water/electricity resources, items, equipments, caps, and a chance to find a new dweller aswell,
10) Edit/Organize mode feature:
Pauses the game! Then allows players to arrange Rooms more effectively and effeciently, and not only for rooms, on this mode players can also get a fullview of their dwellers where player can easily change name and equipments for dwellers their dwellers, (in the early stages of the game it was easy to manage the dwellers and i know which and where the dweller is im looking for, but on the late stagrs of the game once i got 150+ dwellers, it simply became tedious and really hard to manage the dwellers because i have to keep scrolling in a very long list of dwellers, im sure yhat can be improved by devs
Those are my top ten suggesstions, i just love the game and would like to see it become better and be the best, im currently playing fallout 4 and having a blast! More power to all fallout