The Fo3 feel comes from the fact that the whole DLC is heavily centered around exploration of of empty or dungeon like location, with other features that come as side aspects.
I wouldn't call the caves in HH "empty" at all. There is always something useful to be found- either information on backstory, or somewhat unique items or stuff you need in the DLC. As far as I can remember, there was not a single cave "just because", unlike Fo3 that was sending you through annoying dungeons with the only reward being some stupid stimpak.