Which tracks from the Morrowind soundtrack get used specifically?
Various mx_explore tracks, and they seem to be straight transfers, not remakes. Pretty sure mx_explore_2 is at least one of them, and maybe mx_explore_4 but need to play a bit more for them to pop up. So far, don't recall hearing mx_explore_5 yet; it's pretty noticeable, usually. A few of the peaceful tracks in ES V are specific ones from ES IV, as well, if my ear rings true, but the ES III ones stand out more.
TBH, this import was likely a direct response to all the ppl who mentioned ES III's music (specifically the exploration music) as one of the many, many, MANY areas that ES IV fell flat in, when compared to its predecessor.
It seems as if Bethesda listened REALLY, REALLY hard to the fans, but also managed to still move forward with new ideas (major kudos to them for either, and huge kudos for managing to do both and make it work!). While they did not copy ES III, they managed to work the same themes. Witness other areas of fan complaint in ES IV:
The night sky art (note the INTENSE Borealis in Skyrim now, tho the stars themselves are a little dull)
The lack of challenge to exploring in ES IV since the land was nearly all flat, as opposed to Vvardenfell's maze of mountains (Skyrim being the perfect place to have mountains, of course).
The simple grand, tho stark beauty of Vvardenfell, which Skyrim answers with gusto in its more familiar, but amazingly awesome mountain ranges.
The ES IV hero was a zero. Martin was the real savior there. TBH this was more a problem with rising expectations, since ES I and II heroes were also basically lackeys in many ways. ES III broke the mold, and it's hard to go back to a nobody after having a hardcore savior as the character. Skyrim's hero is beyond even that, being in the same mold as Talos himself.
P.S. edit: Followers are likely a direct response to all the companion mods for ES III and IV. Bethesda did the smart thing and realized that the best clue as to what players really want is to see what they go through the trouble to mod themselves.