As I sit here in the airport lounge, thank you 2 hour flight delay, I would recommend people temper their expectations.
Not that the game isn't really cool and I truly believe the attendees will have a great time with what they do, but because unfettered expectations almost always lead to disappointment. I know the attendees with be having interviews with the Dev team. I know they'll have 2-3 hours of hands on game time. I don't know if they will be capturing video in game, but I doubt it (not sure of this though) as the team is still bug fixing & optimizing. Releasing new video that potentially could include bugs that are or will be fixed (as the builds would have been made 2 weeks go to be ready for last week's event, bugs may already be fixed), is misleading.
Will the event be cool? Yes. This is the first hands on gameplay for press and, after the embargo lifts, they'll give their opinions on what they play. I am confidant they will love the game, but you will have to wait for their articles, interviews, etc to see what they think.
So, be cautious, be optimistic, be eager. However, also be sensible in your expectations. We have months to go before launch. This is an important event, but it isn't the final Witcher push just yet. Plenty more to come.