This is how would improve the experience of W3 over W2
Coherent weapon and armour stats.
I have already finished a preliminary mod for W2 that makes swords more equal in stats, with certain types having different strengths and weaknesses (for example elven blades does less damage but more bleeding).
There is no reason why for example a Kaedweni blade should do twise as much damage as a Tamerian. Named (unique swords) are significantly more powerful.
This could of course be changed if there is a lore reason for blades from certain regions being more powerful then others. And too many powerful items just causes inflation in our appreciation of gear. Specific gear for specific situations that allows you unique advantages is a much better alternative then to just get replacing your armour and sword for the 11th time.
Realistic crafting, inventory and weight of items
Lets hope for an end to grinding just to craft stuff. W1 did it right, especially when it came to Ravens armour. ”Dark items” in W2 did it wrong. When it comes to ”legendary items” you either re-assemble or re-make something from special original pieces you find during quests or your travels with the help of a master in the appropriate craft, or you get the stuff as a reward for completing a very special quest. A smith with proper specialisation creates weapons and/or armour, not a hunter (who could be good at making bows and traps) or trap-maker. And lets rid the game of Geralt carrying more stuff around then what would actually fit an some pockets and a satchel. Its silly with an inventory full of swords and armour. You could have a dagger and an extra additional weapon hanging from the side, but I would like to see movement penalty if Geralt is carrying much more then a standard armour and two swords, a dagger and some herbs and potions. Potion brewing was also handled better in W1. (bring back booze and camp-fire potion-crafting)
No newbie witcher.
Character development should be about new paths that go beyond the already established abilities. Geralt should not be needing books, tomes and scrolls to know stuff about monsters and how to prepare potions, unless it is about something very unusual and unique. Imported character should start with a few levels extra or simply at the same level as when finished w2.
Geralt is an experienced witcher and both an excellent swordsman as well as subjected to extreme mutations, even by witcher standards. That is why there should not be different ”paths” in character development in a way that basic moves and mutant features are ”unlockable”. All versions of Geralt should of course know how to riposte and so on. Character development should be focused on other areas that are not covered by wither training, but comes from learning from his interaction with the world.
For example, Geralt might become a more capable alchemist and might improve or modify known potion-formulae through Kalkstein teaching him, and the same can said for Triss teaching giving him a not dramatic but still significant boost in his command of the arcane (stronger signs and perhaps even a simple spell that goes above mere signs, we already had that in w2, the ”heliotrope sign”, which unfortunately was called just that:the heliotrope sign when it was not, in fact was a spell that manipulated time. )and Ves sharpening his knife-throwing skills.
Realistic damage
Lets put an end to useless weapons, against unarmoured people and monsters in particular.
Unless there is a lore reason for it, a silver swords should slice unarmoured monsters like nothing, especially those soft looking drowner chunks of wet walking flesh. Higher damage output by Geralt can be compensated by enemies sometimes attacking in greater numbers, more aggressively and from different directions. This applies to everything from drowners to human bandits.
Realistic and appropriate merchants.
No witcher potions etc in their inventory. Why would a town paddler have potions that would kill ordinary people? Sure perhaps a town witch or specialist in herbal medicine would have potions that ordinary people use to treat ailments and other medical conditions in small doses that could be useful for a witcher to neck, but unless this is exactly what potions like Swallow etc is, it should not be called those names.
Unique npcs.
Especially those you can interact with up close in dialogue. I know it is a lot of work, but why not use a simple customization program( like those we see oblivion or skyrim) or give 3d-artists among the fans something to do, or both.Morphing of different models could also be utilized for small communities and families (a sign of inbreeding or family resemblance)visited by Geralt.
Also I would like to see an appropriate difference in npc skill and ability in battle. This was a bit problematic in W2 as Letho was in fact not fast or had any unique moves, and Saskia should, unless she is as weak as a ”regular” woman of her age, of course have been more then a match for Henselt in a duel. (shouldn't she really beat the crap out of him no matter how much you try to fight her?)
Npcs should not repeat themselves (”-I think the stew is ready..”) and new dialogue should be unlocked as time and events progress (for example, instead of repeating the same old line about the stew, they could discuss how good the stew tasted and when the Kayran having been defeated and that someone should try and get some of its meat or something). I feel it is important for characters you can talk to to be able to talk about major events, especially those they have played a major part in. For example, I missed not being able to talk to Dandelion after ”With Flickering Heart”.
Better combat movement.
Sidestep/dodge is an important combat feature missing in w2. It would also be awesome if there were different combat animations for blocking and attacks depending on position, situation and type of attack. If so, combat could be more like in cutscenes (take the final Geralt vs Letho cutscene as reference).
Better quest interaction
Introduce side-quests where there is time to do them. I find it hard to go on treasure expeditions under Loc Muinne when I am either in a hurry to find and free Triss from a torture chamber or have a top summit to crash with no time to loose. Ideally, they should have solved it with something like it being night after you had freed Triss and that the deliberations and meeting was to continue at noon next morning. Speaking of which, in a realistically scaled game-world, day cycles can be a bit longer.
Real stealth.
Sneaking that can be toggled. Bodies that can be moved and people react to if found. Some kind of trespassing mechanic that gives you a bad reputation if you are found to often in places where you are not supposed to be. No stealing without consequences and stealing should be limited to specific and meaningful choices.
And.. Realistic loot.
save for hidden objects (stuff that fits in pockets, worn around the neck and so on) what you see is what you get. An armoured knight is should not carry any witcher potions or extra armour suited for a witcher on him, and so on and do forth.