Deltarune Chapter 1 is a great first introduction to the characters and gameplay. It's different enough from Undertale that it keeps the whole experience fun. Also, the characters in Deltarune Chapter 1 are really great. All of them are charming, interesting, funny, and I always wanted to see what was in store for them next. According to the chapter selection screen, there will be 7 chapters, so I suggest getting on the Deltarune train ASAP