So - as a couple of people asked me to let them know how it was...
At this point, it's far too early to make any glowing recommendations - I've just completed the tutorial and am a little way into the non-tutorial part of the prologue, so I'll just put down some observations - primarily detailing differences that have been made since the first game:
You can no longer drink potions in combat - they are strictly for before combat (as in pre-buff) - they also seem to have shorter durations (but it's been a while since I played the first one so this may be misremembering). So - no healing potions in combat... just regeneration ones beforehand if you feel you are going to need it.
The advancement system has had a lot of the redundancy removed - now you no longer need to improve 6 different sword styles - now it is just swordsmanship. You are also forced to wait until level 8 before you can start to develop either swordsmanship, sign use or alchemy. This seems good, as the general talents that you can spend on before this point seem like the essentials that everybody would need (you could take about half of them up to this point).
Combat - no more do we have the chain attacks from the first game (which I quite liked as a system), but we are now on a much more fluid combat system that reminds me a lot of Batman: Arkham Asylum (left click does a quick attack, right click does a strong attack, and Geralt leaps about all over the place to get to the enemy if necessary first). Parrying is now more important than it was, and Vigor (the equivalent of mana) seems to regenerate much quicker - this is good as a successful parry costs some Vigor.
New arm-wrestling mini-game - wow, that's difficult. Quite cool, and makes sense, but will take some practice. It's hard to describe without actually using it though - when I read about it in the manual it made no sense until I saw it in action.
Fist-fights - now use a Quick-Time-Event system, which works really well. Far better than the first time round.
Toxicity only lasts as long as the potions are in effect, so it now stops you from having too many effects at once, but does not limit how many you can take before resting.
Storyline - too early to tell at this stage. What I would say though, is that the tutorial is done through Framed Narrative, but the rest of the game appears to not be. I mention this as I know some people don't like Framed Narrative, and I wouldn't want them to be put off by a narrative device that appears to only be in use for the first couple of hours of play. I quite like it, though Geralt appears to have a certain level of amnesia again... this is less good.
Nudity/Sex - you get a fully nude Triss in the first minutes of play (and by fully nude, I don't mean that she just happens to be nude and you can see her back!), and it is done through the game engine, rather than the cards this time. Despite the surprise of how early it is, it was very tasteful.
Difficulty - I'm playing on Normal, and it's surprisingly unforgiving. At least until you level up a couple of times. In the first game, it was hard to die unless it was either a boss fight or you got overwhelmed (and I mean completely overwhelmed). In this one, three people can be enough to overwhelm you, so you have to be a lot more careful about your fights. I never used bombs in the first game - in this one, I've had to use them already.
Speaking of which, I haven't used them yet, but there is also a trap system.
Quests - be very careful. I played through the Tutorial once, went to the free guide I got with the game for some advice on the boss fight at the end of it and realised that I had missed a side-quest that is intended to go through the entire game with you. Don't go and talk to the king until you have thoroughly explored!
Overall, I'm enjoying it so far. The difficulty curve took some getting used to, but now I'm in the actual game rather than the tutorial, it seems to actually be easier of all things. I should get a chance to play some more tonight, so I'll report back more tomorrow.