My dream game would basically be a huge budget Betrayal At Krondor. The combat would be sort of like Krondor, and Divinity Original Sin, with a hex battlefield, action points, turn based. But as much as I love Divinity Original Sin, I find it quite shallow and also very childish. My dream game would work similar to that but with a lot more depth and a more realistic setting.
Like Krondor, you would explore in first person, and in battles you can stay in first person, or mouse wheel to scroll outwards and upwards, to give a tactical view of the battlefield.
But the game would play like an RPG outside of combat too. You explore the world in first person, the graphics would be stunning and in a beautiful world, like Witcher 3 or highly modded Skyrim. Pretty, but also huge and varied like I've only seen in MMOs, you can go to desert regions, swamps, forests, plains, volcanic areas, etc. In first person, you look down and see your hands and feet, and when you cast a spell, your hands wave in front of you, conjuring the spell. You cast Spirit of the Wolf, and you transform into a wolf which has a much improved run speed, and you set off exploring. There are some side quests, but not many. But there is an enormous main quest that you get hired to take on when you eventually reach the main city.
The game would have a real faction system, where you start with friends, enemies, and neutral people in the world. But you can improve or ruin your relationships with various actions. There would be no savegames, so you can't just reload if you fuck up, so you have to think about what you say to people, and you have to be very careful when travelling. It would work like an MMO, single player and offline, but like running your own server, when you die, you are respawned back at a church and all your characters have injuries that take time to heal, so you will reaaaaally want to avoid dying.
There is also no map, and no radar. You have to explore and figure out where you are going based on your own bearings and by looking at landmarks. When you reach the big city you are hired and given a quest that starts with you investigating a castle far to the north. They give you a hand drawn cloth map with some rough directions, and that is all you have to go on. You can make your own edits on this cloth map as you go. And in new regions you will have to find someone who has a map of that area, or you will have to create one yourself.
All the classes would be completely unique, there would be no Paladins, Wizards, Druids, etc. It would all be unique names but also unique gameplay, something that I researched and figured out years ago when I was a bored stoner.
As you travel there are enemies wandering around, but in more realistic ways. Predators like lions or wolves don't just wander around like game mobs, they hide in the grass and will spot you from far away and will lay in wait and either hide from you, or ambush you. Giants and Cyclopses will act differently, they will charge at you aggressively, etc. Intelligent humanoids use tactics. Bandits hide in trees and jump down to attack you when you aren't expecting it. Unlike an MMO and most RPGs, mobs don't just engage you when you get into range - range being 50 feet. Instead, they have real eye sight, hearing, and animals can track your scent. This means that most animals will hide from you, but some animals and enemies will actively hunt you down, travelling maybe a mile to attack you after they spotted you from a distant hill.
But the player's party has 100+ spells, like EverQuest, not just combat spells but dozens of utility spells, and you can cast any of them at any time. So at any moment you can buff up your entire group's hitpoints, give everyone wolf form (which gives them fast run speed and makes them friendly to wildlife but kill-on-sight to humans etc.) and you can even cast invisibility on your whole group, etc.
When you get into combat, it works similar to DoS, but with 100+ spells and more interesting classes. There is invisibility, see invisibility, damage shields, disease DoTs, poison DoTs, magic based DoTs, Fire, Cold, and everything has resistances to these things so you need to use the right spells in the right way. You can snare enemies, root them in place, disarm, dire charm, sleep, knock down, enfeeble to lower their strength, magical curses that lower their attack speed, and many more, in addition to all the usual attack spells like fireball, ice storm, cone of cold, acid arrow, etc. Basically it looks like DoS, but with all the depth and spells of Baldurs Gate 2 and ToEE and more. And the battlefield extends far into the distance, instead of being just a small area. And say you cast Turn Undead on something and send it running for fear into the distance, it can attract the attention of more enemies that will come and join the battle.
The sad thing is, Betrayal At Krondor did a lot of this already, and 100 years ago. But the games industry has turned to shit since then and is only just finding its feet again now. A game like this could happen again but big devs are depth-phobic, so none of them will make it. And it will take time for the budgets to start improving in indie gaming to the point that they can make some epic RPGs and not fun but primitive passion projects like Blackguards, DoS, etc.
I actually have this game all planned out, exactly how I would like it, but I also have 2 spin offs too. This would be a huge and deliberately hardcore RPG with as much depth as I can imagine. But I also have an idea for an action RPG spin off which would be very challenging and very deep and tactical too, but all played out in real time and in an exciting way. And I know how it could be done because I have played stuff similar in the past. And if either of those games were a big success, I have an idea for an MMO too. But it would be completely unique, and nobody will have played anything like it. It would be the biggest game ever made. It would be hardcore and interesting like Ultima Online, but bigger budget than Star Citizen, and bigger scope. People would live out a genuine alternative existence in this persistent virtual world. Some would be peasants, some would be traders or crafters, some would be adventurers, but some would kings, some would run entire empires that they build from scratch. It would be like EVE online but far bigger, and actually fun.