Over 4 years since I first put it in my 360, I popped the last Achievement in ES 4: Oblivion last night. I plodded along for a while, picking up achievements as I went. I took a character I was no longer playing to the Shivering Isles, just to knock those out. At one point, I made a character specifically to do the Dark Brotherhood and Thieves Guild. I got DB, but glitched out TG and couldn't finish it. Finally, during break between my last two semesters, I made a character who would do everything except DB, TG, and SI, and another to do DB (which I really like) and TG. It took a while, but by the end of break, the only achievements I hadn't finished were the last one in the Fighters Guild and the 3 that I had been unable to get to in the Thieves Guild. And there it sat for about a year - 4 Achievements undone.
Just before Christmas, I decided to fix that. I fired up the character who had done most everything and did the last few quests to finish the Fighters Guild. Then I fired up my sneaky and vowed to get through the Thieves Guild. I played a little each day, finishing quests a little at a time. Finally, around 10:00 last night, my 360 dinged and I became Master of the Thieves Guild.