I've played it on the GC, unfortunately only for about 20 minutes. I didn't even finish the prologue, which is the introduction to the story but consists of nothing but fighting and scripted events so that's all I can comment about.
The story starts like this (spoiler light, because it doesn't really make a difference):
The wounded and unconscious Gerald, a legendary Witcher, is found by other Witchers. After they brought him to their castle and attented to his wounds (which took an indefinite amount of time - possibly weeks), the castle is being attacked. Gerald, who suffers from amnesia, has to help in fighting off the enemy.
Fighting is alright. You click on an enemy with your weapon drawn and Gerald lets off a series of slashes. During such an attack the cursor changes when the time is right for another click, which, if well-timed, lets off another series. If done properly you can make combos that way. If ill-timed the attack stops and Gerald is open for a counter-attack (at least, that was my impression. The enemies never faught back at that point). I had some probelms with it at the beginning, but after the third fight it was quite easy to make combos until the enemy drops dead. Some deadbeats who were too lazy to read through the tutorial messages and any dialogue didn't get it even after 20 minutes of playing. They kept on clicking all the time, diablo-style. They seemed to be quite frustrated about it but after I told them how to do it, they found it quite intuitive. There are also some tactics involved. You can change styles whereas some are suitable when fighting quick, strong or simply many enemies. Gave fighting a nice touch although there didn't seem to be any indicators that told you which enemy is strong and which one is quick apart from the tutorial messages I got. You can dodge attacks manually, by double-clicking anywhere on the floor. All in all well done. IMO better done than any combat I've ever experienced in a RPG with RT combat. Perhaps it's important to add that IMO RT combat in RPGs usually sucks, unless the player has at least some influence on the outcome. Combat in NWN 2 bored me to death.
While the prologue consisted of much fighting, it was much more interesting than i. e. NWN's prologue. There were less enemies, there were some interesting scripted events and the tutorial was incorporated into what happened. For instance, at one point Gerald has to use magic. He has no clue about magic whatsoever due to amnesia and has to learn something about it quickly. When he does, the magic system is explained to the player.
Still, there were some things that bothered me. For instance, the prologue is absolutely linear and railroading the player through the events. Hopefully this is only the case for the prologue and not the rest of the game. I really don't want another NWN 2. For me, that's the most important factor. If the game turns out to be like NWN in this respect, I won't buy it no matter what.
The second thing that bothered me was a "quest-compass". Now, during the prologue it was a good thing and it would be quite awkward if it wasn't there. But if the quest-compass shows NPCs as well - in other words: if it's anything near to Oblivion, then it's the sort of hand-holding I despise in *any* game.
Apart from that, there wasn't much I didn't like. Controls were absolutely intuitive - you can choose right at the beginning if you prefer keyboard or mouse and the controls change accordingly. I can't tell anything about sound, music and the voice over thanks to the Sierra booth which was around the corner, approaching the limits of their sound system. From what I saw the atmosphere was quite good - art design and level design are both great, the scripted events are well done. I didn't see much of the story, but the mood was set and although not much was shown, I already want to know more about Gerald, about what happened to him and about the Witchers (yeah, I've yet to read the books). I'm quite positive, all in all.