Before I built a gaming PC I played Oblivion on my Xbox 360. I started playing Oblivion around 2008, which was late to the party because I had just started college. I beat the game entirely, save for the Duke/Duchess Quests which you could only choose one. My last achievement unlocked was June 15th, 2009. Well today after rejuvenating a character I hadn't played since 2011, I played through the Shivering Isles quest line one more time to finally unlock all 60 achievements!

Has anybody else recently gone back to get the final achievement after putting the game down for a while?

No. I don't have any Achievements. But, congratulations.

Considering I play the PC version, I won't ever get any achievements. But if I could, then I would probably get them naturally as I play, like I did with the 360 version (possibly the first game ever where I got all of the achievements). Unlike Skyrim, all of the Achievements can be attained without doing anything crazy and pretty much just following the main questlines. I'd probably only need to get the Thieves Guild/Dark Brotherhood achievements given what I've played so far.

Anyways, congrats.