The problem with Oblivion's (and especially Morrowind) music was that you only had a handful of general purpose songs that just feel repetitive and boring after a while because you're listening to them so much. I hope Skyrim gets more variety like different explore music for different regions, and different types of songs for crypts/caves/ruins etc instead of general dungeon music.
I would turn off the music after a while, if there was more prominent ambient background sounds to help set the mood. Both Morrowind and Oblivion were lacking this.
Not repetitive at all, by the very word's definition. Every piece of music was crafted, more so in Morrowind than Oblivion, I do not see why you'd think repetitive. Also, I don't think the music loops but rather fades away. (some composers really make repetition their staple, and use looping music until combat is over.)
As a second point, exploration and combat music should be unobtrusive above anything else. The main theme should be memorable, and it is. If you create overly-intricate, structurally complex music or, in fewer words, drive away the attention of the player then you have not succeeded. A film composer who does that equally fails. Ultimately it may be about taste or preference, for which there is no argument that makes sense.