You have to Demo your game... Was The Witcher 2 "spoiled" in some way because they showed the Introduction to Flotsam sequence during E3? Since Developers rarely do "proper" playable Demos these days, they have to show enough footage and provide enough information so people feel comfortable enough making a purchase. Obviously people could just wait for reviews and/or trusted user impressions, but it's pretty much the typical AAA trend these days to show off your game enough to get as many Day 1 Sales & Pre-Orders as possible.
They're probably showing off more than they ever did with the previous games, at least in terms of Raw Gameplay. However following the style of marketing they're going for, it's necessary, the 35 minute Demo is necessary to show off how The Witcher 3 approaches Storytelling and Cutscenes, which is one of the most important (arguably the most important) parts of The Witcher series.
If you're a fan and know that your pre-order and day 1 purchase is assured without seeing a single piece of footage, then simply don't watch the footage. However even in the Demo we saw, only one dialogue selection was ever taken, and there's a major choice at the end which gives you another option and a path in the quest that isn't spoiled, and the Intro is hardly what would be classified as a Spoiler.
I think everything they've done so far has been perfectly fine. I just hope that future footage focuses on specific aspects of the game (Alchemy, Combat, Mini-Games etc) so they can use little random snippets of footage from the world and not show off another Questline.
