In addition to the untoggleable Exp. Share (which carried into SwSh and BDSP), LGPE are the first games:

In which not every Pokémon revealed at the time is programmed into the games. (i.e. Dexit)
To have a decreased amount of TMs available compared to past games.
To not have any battle facilities since Pokémon Gold and Silver.
To not be compatible with previous core series titles in any way since Pokémon Ruby and Sapphire, and as such, the first to be unable to trade with other core series games in their generation.
To not feature Wonder Trade since Pokémon X and Y.
To not feature breeding since Pokémon Gold and Silver.
To not feature Abilities since Pokémon Ruby and Sapphire.
To only have regional Pokémon in the main storyline since Pokémon Black and White.
To not be compatible with the Pokémon Global Link since Pokémon Black and White.
(info from the Bulbapedia trivia page)