The Super Mario Galaxy + Super Mario Galaxy 2 bundle for Nintendo Switch features upgraded visuals, new control options, and extra content like new storybook chapters and an in-game music player. Both games retain their core gameplay: Mario explores various themed galaxies, jumps and spins across planets, and collects Power Stars to save Princess Peach from Bowser. New additions include an Assist Mode, a combined physical release option, and updated UI.
You can watch this video to see an overview of the bundle: