The Giver could have been an excellent movie. At the time when the book first came out, it made a major impact as a YA dystopian novel. There wasn't much around like it at the time and a lot of other, more recent books, actually take a lot from it. Unfortunately, as The Giver is being released after movie versions of those other books, it's bound to be seen as derivative (or at the very least, all of the tropes are now well saturated in the YA market which takes away the impact of them). It's kind of the John Carter effect all over again. People thought John Carter relied on too many common sci-fi tropes... but the fact of the matter is that it was responsible for popularising a lot of them over the years.
With The Giver, the movie adaptation also suffers from the filmmakers' apparent need to bring it up to the 'standards' of the modern YA movie. Case in point (and no spoilers for the movie, specifically because this is material from the trailer), in the trailer it is stated or at least implied that Jonas - who is eleven in the book, btw, certainly not anything like as old as the actor playing him - finds the giver because he's doing something rebellious and going where he ought not... because rebelliousness is obviously a necessary trait for a YA hero. In the book, he is assigned to be the Giver's protege. The trailer also implies a lot more action and tech/explosions then there were in the book, which is honestly a bit cerebral at times. The greyscale to colour jump is in keeping with the books, but the trailer doesn't do a good job of making it clear why this element exists. (In and of itself, the use of greyscale and colour in such a manner is not without precedent. See Pleasantville.)
Overall it's just highly disappointing, especially considering some of the cast members are actually well fitted. The Giver could have been a good movie and a good adaptation of its source material. Done right, it might not have been a major box office success but could still have been a critical one and been a possible award winner (as the book was). Instead they watered it down, added overplayed YA tropes and basically made it into a movie that is The Giver by name and doesn't capture the spirit or intent of the original.