Oh don't get me wrong, Witcher 3 is fucking amazing. I'm just saying it's better to temper your expectations and be pleasantly surprised rather than expect something of that caliber again and be disappointed. A completely new project is wildly different than developing a sequel to an existing one. Look at how popular the Saint's Row franchise was, and then how lukewarm the reception for Volition's next project (Agents of Mayhem) was.
Tl;dr: I am hyped, want the game, but worried about progression vs size\scope of the game.
Or long version, the way I look at it is
Witcher 1 - Very large game with a focus on story production values that, at that point, hadn't really been done to my knowledge in the top down somewhat hack and slash genre. However, had quite a few issues. They listened to that feedback and continued updating it with free updates to an enhanced edition.
Witcher 2 - Continued the style of one. Taking feedback from the first and making it much better and even larger. Focus in particular was in expanding dialogue, side quests and adding "character" to the world. Still had issues, but again, listened to feedback and a dev even made an unofficial official patch for it and later an enhanced edition was released as well (unless that was for the first one, can't remember)
Witcher 3 - Continued the focus in creating a world with character development and production value as a factor. Which at this point still stand head and shoulders above any other RPG in the genre. They also listened to feedback which this time came in the scope of one great DLC/expansion and one good enough that it could be a stand alone game and still GOTY material.
Point being, CDPR consistently made upgrades of their games, focusing on the story and the game world. Their end product of that progression still doesn't have a peer four years after the release. Hence, my faith so to speak, is fairly high when it comes to their skill and knowledge in putting a world together.
However, the downside of their previous games was the same in all the games. The combat and loot progression. It continued getting better with each game, but I finished The Witcher 3 and both DLCs on the hardest difficulty, and it was still a joke from around the mid part of the game. It was very easy and the same skills\playstyle from around hour 50 to 150. Armor and weapon upgrades after you started getting the set you wanted was non-existent, which was about halfway into the game.
Still, I assume it is "easier" to develop a good FPS combat than it is to develop good melee combat. There aren't many melee games that lets you instantly swap weapons tactically. You don't go in with a longsword do a few slashes, switch to a mace for a stun and finish of with a combo from a dagger. However, going from rifle, to up close with a shotgun and finishing an enemy off with a combo headshot from a gun... Other than perhaps the last combo, that is something we do in games all the time. So I also believe they can make that aspect good. Certainly looks like it from the gameplay trailer today. Should also be easier to add a larger base of loot to the game with implants, armour, and weapons that aren't just "sword +1"
That said, my main concern in this game is the same as nearly every single large open world game. The amount of content makes it so that you progress past a large part of it. I always do all side quests before progression, but that always leads to me getting demotivated around mid game because it's not even remotely challenging anymore and there isn't really any character skill development left. You just putting any eventual skill points, ability points or whatever into things you don't ever use.
For example for this game. How long until you get the military grade plugins\guns and what do you have to work for after that? Enemies have levels, if they don't scale, how long until you progress in experience so far that nearly everything you encounter is grey? How much "content" is left at that point?
So my worry isn't that CDPR can't make a new massive game with a new IP. It's that they won't fix the problem that no developer has ever fixed. The Witcher 3, while still my favourite game of all time, was absolutely horrible in that regard. And the problem there is that I finished TW3 completely based on me wanting to see everything Geralt had to offer. I wanted to conclude a story built on several games. Between the games I had been hearing about Ciri, Triss, Yennefer and Geralt for years. It certainly wasn't the trivial combat or the lack of any loot that made me finish it.
This game doesn't have that. So if progression falters mid way, it might end up the same as Fallout 3, 4 and Skyrim. I've never finished the main story in any of those. 100s of combined hours, but every playthrouh ends not long after I quit caring what loot dropped or if I level up.