Oooh, these are two very fine tracks! Gotta be honest, the underworld theme to me sounds more like a tavern theme or something, but it's such a fun track that I don't want to complain about that too much. I also quite like how the somewhat blues-y end of the overworld theme hints at the underworld theme.
The one thing I think the tracks lack is just a tad more variation. Maybe mix up the instrumentation a little somewhere or add a few fancy chords here or there. But overall, really good job!