I have no clue what this is going to be, apart from what the video says, but it certainly looks interesting. The stories in the world of Pokémon that this series will cover appear to be in the primary canon – that is, in the canon regarding the games, and not the anime. The animation style seems to be identical to that of Pokémon: Origins (which is now playing on the official Pokémon YouTube channel), which I consider to be far superior to the everyday anime starring Ash Ketchum and his friends. One of the more interesting things I saw in this trailer was what appeared to be some sort of raid, likely conducted by some sort of Pokémon SWAT team.
Whatever it is, Pokémon Generations certainly promises to be interesting.