I must disagree with the OP on this one.
I find:
1. Mercantile and Speechcraft.
2.Acrobatics and Athletics.
Both of these were alot of fun for me, I enjoyed working up my speechcraft with NPCs to see what else I could get from/with them at higher reputations, owning a shop wasn't as fun as it Could have been, but it was nice.
Acrobatics! I jumped all over the place, and as a ranger I found great utility in my improved ability to jump a little higher, a little farther. Often times I could get to spots a ground-enemy couldn't reach as my skill improved, and I felt BGS did a Great job with this skill in Oblivion. Athletics - affecting how fast you run, again something I very much enjoyed. At high atletics I could almost outrun a horse and could out-run many animals when exploring between towns.
I think this is a case of different strokes for different folks - we all have our desired playstyles. I think Bethesda did very well with these skills in Oblivion, and look forward to seeing how they improve on them with Skyrim! :goodjob: