I've watched trailers but not all the gameplay videos that have been out. I watched the very first one when I was trying to compile a list of features but now I feel like it is all in the open and I rather do the actual exploring and figuring out some of the open-world puzzles myself.
It definitely has gone beyond just teasing, although I don't feel like they have particularly spoiled most of the game. I think the amount liberated till now it is perfect. They have been really good at handling things, giving us a long starvation and the sprinkles that were kept in Crescendo right up to the Switch Presentation Third Trailer. I don't think they will add more, or at least I hope not, because if they do then I'll have to share your concern for this over-exposition of the game.
Usually, the stuff that feels overkills it is not Nintendo but the same fans overanalyzing things, like when they deciphered the Hylian language on the Tapestry and have found out what it says (which seems to be a prologue). That information, for me, is a big spoiler.
I feel this game is a call to the Zelda fans, including the old schoolers that never completely saw eye to eye with the 3D games. BotW seems like a second take on the original idea of what they expected Hyrule Fantasy to become back in the 8 bit era but without the limitations back then, and they have stacked everything quite high. Adding voice acting is probably one of the ballsiest movements.
I'm glad they've stuck to in-game footage rather that pre-rendered crap like most triple-A companies.
QFT. Nintendo is of the few that actually show gameplay. I hope they don't change that.
