More than 100 new Pokémon.
There are indeed new evolutions and pre-evolutions, most of them focused on Gen V Pokémon. However, a few older Pokémon, including Gen I classics, are getting surprising new developments.
No new types, but there are “Cross-bred” Pokémon introduced. Certain father/mother breeding pairs will result in a visually distinct child, who will be the mother’s species, but will, for example, have a pattern reminiscent of its father or a slightly altered color scheme. This is basically the new Gender Difference and is simply an aesthetic bonus, nothing extreme and only certain pairings result in this…the Pokemon is still considered the species of its mother, it’s not a new species. One example I can give is that it is possible to get certain Pokemon sporting Pikachu’s red cheeks.
The Starters become Grass/Steel, Fire/Psychic, and Water/Electric. They’re inspired by various European-centric archetypes…Chespin becomes a knight with chestnut armor, Fennekin a wizard with a majestic fur cloak, and Froakie a Nordic Viking with a thunder-cloud mullet/beard combo.
Xerneas is Ice/Steel, and Yveltal is Fire/Dark. They have a unique ability where they can shift types with each other, Xerneas becoming red and Fire/Steel, and Yveltal becoming blue and Ice/Dark. Supposedly, Game Freak chose the typings in part due to members of the team being fans of R.R. Martin’s A Song of Ice and Fire, among other reasons.