Before this episode, all what was knew about her was what Simon Petrikov said in his video diary revealed in "Holly Jolly Secrets Part II", leading to many unanswered questions that created a lot of speculation and all kind of theories among the fandom.
Like "Holly Jolly Secrets Part II", this is a very revealing chapter, solving many of those unanswered questions from an optimistic and hopeful perspective which ends with the promise of a continuation. My only minor complaint about "Betty" was the pacing: 10 minutes is way too short time to deal with the whole Simon/Ice King, Betty and Marceline story arcs, and it would have been nice if this has been a two part special as it was originally planned. However, despite that, the result was still highly satisfying and it was delivered in the best possible way, considered the time restriction.
I just hope to see more of Betty and Simon in future episodes of the series.