The quick version - this game is simply head and shoulders above any other RPG. If you have any interest at all in this kind of game, then do not hesitate to buy it. If you're not off ordering it, read on...
CD Projekt have created a complete, living and breathing world rich with detail and more `real-feeling' than Bioware or Bethesda have managed before. The world of The Witcher feels `old' and lived-in with a real sense of history, where Bethesda's and Bioware's worlds just seem like a framework to hang the plot on, and go adventuring in.
The entire game world is not `open-plan' like `Oblivion', for example, but rather a collection of huge `open' areas to explore. I'm not sure if they can (or need to) be returned to once left, as I'm only beginning to scratch the surface.
Because of the sheer depth of the world and gameplay, The Witcher 2 (TW2) can be a daunting experience; you do NOT play this game - you IMMERSE yourself in it. If you're not willing to completely involve yourself in this world, and commit to the game, you'll struggle. The game expects you to read the manual BEFORE playing - a crazy idea in these attention-deficit, `drop in, drop out' gameplay days. It also expects you to read through the tutorials in your in-game journal as they appear; this is a complex and rewarding PC RPG - not some crappy, dumbed-down console game that will hold your hand all the way through; if you can't be bothered to prepare, and read the literature and help provided, that's not the game's fault.
Every new location you enter, new person you meet, new monster you encounter, or even conversation you have adds new information to your Journal; enriching it with backstory, or adding to your knowledge base. Sometimes, you'll learn something from a character you may not think hugely important - even if it is to do with a main quest - and it will be added to your journal; on reading the journal entry you'll see it actually expands on something said in the conversation which might not have been obvious. I find myself checking my Journal every ten minutes or so, and it actually works as companion to the game, not just somewhere to store dead conversations.
Also, the need to check the Journal frequently and be so reliant on it is no chore at all; in fact it is a pleasure, simply because of the manner in which it is written. Each Journal entry reads as if your adventure is being written up years later by your trusted friend Dandelion the Bard, so it reads like a novel. Dandelion adds his own personal (often humorous) observations, and documents Geralt's (the main character) thoughts after the fact, which is where the need to read carefully for subtle clues and further information comes in.
TW2 expects you to think and prepare before sending Geralt into a situation. The best example I can give is this: Let's say you're given a mission to go and kill some monsters (Nekkers) by an NPC - a standard RPG cliché. In a normal RPG, events may unfold like this:
NPC asks you to kill the Nekkers> You ask him about Nekkers> He says something like "I hear they don't like fire. Willy The Wizard in the Town Square can enchant your sword with a fire-spell!">You go to the Wizard (possibly doing ANOTHER side-quest before he'll help)> You get your sword enchanted>You Kill the Nekkers.
In TW2, it'd go like this:
NPC asks you to kill the Nekkers> You go and try to kill the Nekkers> Barely escape with life> Consult Journal> Journal says you should research Nekkers> Go and buy/steal a book about Nekkers/question the locals>Find out Nekkers don't like acid> Get/Use formula and ingredients to make acid bombs> Go hunting Nekkers.
In fact, TW2 doesn't expect you to even do steps 2 & 3 - they can be avoided if you have the good sense to do your research about any creature you've never come across before.
Graphically, the game is stunning - even on the lowest setting. None of the locations seem like a `stock RPG setting'; no two interiors look the same. In fact, no two TREES even look the same so far - I simply cannot describe how real and diverse the environment looks and `feels'.
Only down-side for me so far as I enter Act 1 are the forced Quick-Time Events (QTEs). These just don't sit right with this style of game and detract from my enjoyment, personally. I felt like I was being rushed through the prologue on rails and subsequently missed some side-quests simply because there seemed to be no natural pauses in events, but the quality of the voice and (yes) model acting, and extremely gripping story more than make up for it. I have never EVER felt pity for CG characters in a game before now, and I often found myself amazed at the subtlety of the facial expressions of the characters, saying more than lines and lines of dialogue.
A word about morals and how the game makes you feel. Yes, Bioware games make you responsible for your actions, and your decisions can have consequences down stream. Sometimes they even gave you little sliding bars to indicate how good or evil your character was being. Far-reaching repercussions of decisions made are nothing new in RPGs, then; but note the wording I used; "your CHARACTER"; in a Bioware game (or other RPG), I click on a `bad action' and my characters `alignment bar' may change, or his background picture may darken; the ending of the game may alter slightly - big deal; maybe I WANTED to play a bad character, so that's good. In TW2 I don't agonize over decisions because of how they could effect the game, or my character, but ME personally - that's how involved the game gets you.
No other RPG has made me actively avoid having to kill a character because *I* sympathised with them; No other RPG has made me break off in the middle of a side-quest to consider how MY choice may be affecting an NPC - not the outcome of the game, or the `reputation score' of the character I am playing, but the livelihood and well-being of a CG Game NPC. Seriously.
All this, and I haven't even scratched the surface of the game yet.