Genuinely excellent. I enjoyed how reserved and tasteful the whole thing was, it had a really solid grasp on what made the original Undertale great. The major characters take a little longer to grow on you than Papyrus or Undyne, I'll admit, but I ended up caring for them a great deal. I was really impressed by the authenticity in the smaller details, all of the flavor text was pitch-perfect with Undertale's sense of humor. The battles were really challenging at times, but I never felt unfairly stuck on anything. Undertale Yellow starts off a little slow, but give it time and it'll really impress you.