Both games are very similar to one another. In them, you travel through a parody of the United States. Each game contains different characters, though the overall premise remains the same, and the two main characters Ninten (Mother) and Ness (EarthBound) are very similar to one another.
The emphasis on the fact that the original Mother was present in the game wasn't as high as many had assumed it would be. When promoting the game, Nintendo rarely advertised that the original game was present, and wanted people to be sure that Mother 2 from the Super Famicom (SNES) was in the game. Promotional items were all based on themes from Mother 2, while characters from the original game remained untouched.