As a person who has played Dungeon siege 2, I feel DS3 was a step in the wrong direction. Although I appreciated the lore that came with it(mainly because I haven't played DS1), I was underwhelmed when it comes to gameplay. Personally, I believe it would be better to start off fresh from where DS2 left, and add RPG elements like those in modern games, while still preserving others that made DS2 what it is.
Since DS2 has been released long ago, a new DS4 made with DS2 in mind could very easily relate with it, but it wouldn't be obvious from the beginning due to the new content, except the identical lore and maybe returning characters, from DS2 and/or DS1, depending on the setting and the story progression.
For a start, the game could be made open-world. Seeing The Witcher 3 going from a dungeon-crawling-like game to an open world makes me think DS4 could follow the same path. I wouldn't want it to become a Skyrim clone or whatever, since that was a bit too thin for my taste, although pleasingly large.
My ideal DS4 would be a bit like this:
- Be open world. This could include decision-based changes in npc-player interaction, the usual day/night/weather cycle(and possibly seasons), shops/inns and lowly-mortal features like traders/stands, taverns, features that can exist in a magically-enhanced medieval setting that take away the idea of a world that rotates around the player, but acknowledge the player's strength and growing ability to save the world. Getting praised all the time in DS2 from characters I have never seen changed a lot when I had to create makeshift classrooms in Skyrim and have all the peasants sit down and be enlightened about the 'Dragonborn', and the minor dragon inconvenience. There should also be a period where the player is frowned upon for an action he either didn't do, or was not understood(like the king's assasination in The Witcher 2, the second cataclysm in DS2 where the player is blamed for destroying the world, etc). In DS3 I did not feel that the charcters were really tied with the world, as they were either not known, or lightly looked down upon by close-minded Ur-Shamesh and residents of Stonebridge that generally did not give a damn.
- Keep the 4-6 followers of DS2
- Take a manual combat system(I'm not sure how to call it) like DS3, or even better, hinting at TW2's combat system, instead of the RTS DS2 was. Also keep the ability to switch controlled character.
- Expand the reagent system into crafting, and introduce alchemy (but maybe not enchanting, to differentiate truly magical objects from mundane ones)
- Copy(and improve) the lootfest DS2 was, and make it rewarding by adding rare magical items that would be unobtainable by crafting, especially if enchanting would be omitted.
- The player character should be customizable like DS2, and dialogue could be adapted to make the player seem more like a real character instead of an abstract world-saver entity(getting called a 'mercenary' in DS2 got boring after a while). This also removes the need for preset characters and the need to alter the story to try and fit with each character's story.
- Have a skill tree like DS2, and also its gear management. DS3 characters felt like second-hand cars to me.
- Have the equivalent of new game+, with not only larger numbers when it comes to damage/health/etc, but have certain monsters, like bosses, have different/additional resistances/attack patterns/etc in each difficulty, forcing the player into a new challenge instead of only looking at increased stats.
- Have some epic story and a big danger to go with it. DS2 had the cataclysm and Valdis' conquest which affected the game greatly, as well as the return of the Familiars in DS2:Broken World. The only large-scale event in DS3 was archons falling from the sky, and unlike DS2, the only one who was affected was the player. In DS2, the "catastrophe" had a visible effect in the world, for example the two sieges, the city of Kalrathia being occupied by the Morden and freed by the player during the rebellion, and the great cataclysm. DS3 was just a small story about something that could've been much larger. I felt like I was doing chores for the 10th Legion, which was no longer a legion, but a 3-people clan, and it seemed like I ran into Jane Kassynder's forces on purpose instead of being hunted down.
- Also get Jeremy Soule to make the soundtrack
This is just my personal opinion, I know making a game is not easy, but there are some things I would really love to have them implemented.