HeartGold/SoulSilver media have shown that there are some Crystal features in these new games - seems like the significant parts of the game are in it. That is, every significant part that isn't Kris (not included for unknown reasons), or isn't the PokéCom Center (replaced by Wi-Fi).
So we've seen a few things so far:
Suicune's importance - the story seems to have a focus on Suicune when the player enters the Burnt Tower. Suicune has some extended time observing the player (like in Crystal!) and doesn't appear on the Town Map (nor does the description of the Town Map talking about roaming Pokémon state its name - only Entei and Raikou's names).
Eusine's inclusion - Self explanatory - a Crystal character.
The Battle Tower? - there's clearly a building west of Olivine City. There could even be a Battle Frontier - we don't know yet. West was where the Tower was in Crystal, so maybe this could be the Tower as well?
So, some people think that including these changes ruins the authenticity of these remakes. What do you think?