I gathered a new info from this polish Q&A (made by the guys who played the game, without RED's participation) and articles from unrelated websites for the sake of clarification about certain subject matters. Some of it you may already heard about, but I'm sure there will be some new things for you as well.
- there are many different types of additional weapons that you can pick up. What's interesting, you need a higher level in order to be able to use it
- weapons (including swords) will not last forever and can end up dull if used too much, which will result in minimal damage. You need to regularly pay a visit to a craftsman to maintain it
- HUD is very customizable. There are several options available, including turning off minimap and all sorts of notifications if you so desire
- all graphical settings are present in in-game menu
- enemies will parry crossbow's bolts with a shields
- skill tree is really massive. There are 5 trees (according to witchersite there was 4, so I'm not sure who is closer to the truth), each has 5 tiers and each tier contains 5 skills. Every skill has 3 or 4 levels to unlock. Even though later Geralt will gain more skill points per level it's still will be impossible to unlock all of it
- after unlocking the skill it needs to be activated. You do that by putting it into separate tree, which contains a limited number of slots (it will increase with character's progress). Activated skills affects Geralt's fighting style. Activating set of skills from the same category will increase it's effects. It adds another layer to preparations and tactical planning, as you have to choose an appropriate set of active skills depending on what kind of opponent you going to face (for example, if you going to fight with heavily armored knights, you can activate Igni upgrade that allows you to melt armors)
- there are four slots for mutagens, which also affects your abilities
- temporary companions are quite helpful and even use different fighting styles. For example, one woman that accompany them waited for a right moment while enemies were focused on Geralt to backstab them for massive damage
- game is pretty difficult, as you can die even on easy if you're not careful
- some details about dynamic weather: there will be snow, different phases of day/night, different stages of cloudiness, storms, a few types of rain and even a morning mist
- enemy AI is really good. Wolves and bandits spread to cut off all of Geralt's escape routes. If you kill their respective leaders, they end up completely disorganized. One enemy can use himself as a living bait to give the rest of his squad a chance to put Geralt in a corner If you set up a trap or Yrden sign in front of the enemy, he will avoid it
- NPC's models are very diverse and interior of every hut looks different, so there will be no feeling of deja vu
EDIT:
Now there are some details I forgot to mention. Nothing major, but still something that I think was pretty interesting.
- in gry-online video about combat one journalist said that Geralt still can quickly beat the distance between him and enemy by jump attacking him like in The Witcher 2, but difference is that he's not doing that automatically this time around. You do that by holding light attack button, which is useful to catch fleeing enemies, if you choose "no survivors" policy. That's pretty cool, as it gives you a more control over character without taking anything away.
- in the pclab interview REDs also mention that this time you can throw away the quest items. To make sure that you won't accidentally get rid of something important and thus make the game unwinnable, this things will always remain in a game world where you left it, while regular stuff will vanish after some time. I know some people complained about lack of this option in The Witcher 2, so there you go
- there is one thing I'm not sure about. In the Onet article there is a sentence: "For example Igni sign has four levels, each with unique perks, one of them is armor melting". It may be my misinterpretation, but I think it means that each skill level is like a different skill and you can switch between all unlocked levels of a skill for other bonuses, like one level of Igni allows you to melt armor, but another gives it a wider range and so on. Again, that's just my interpretation of this one line of this one article, so don't quote me about it
- and finally we have confirmed return of another Witcher 2 character. Don't click SPOILER if you don't want to know who it's going to be.