If you're new to this title:
Oblivion isn't a game that you play. Oblivion is a game that you conquer.
Yes, the graphics and mechanics haven't aged well. Yes, the dialogue is often hilariously unhinged. And yes, the game is ripe with bugs and quest breaking sequences that induce a paranoid amount of saving. But its' defects can also be broken in your favor. THAT realization is when the game grips you:
What can you get away with? What cheese tactics, what exploits, or what innocuous and obscure thing (like picking up and dropping a paintbrush from your inventory... this is not a joke) can you leverage to your adventure— and how far can you leverage it? And there's so much to be adventured: every nook and cranny or every dungeon, achieve and ace every quest, grind every attribute and skill to max, collect every unique item, and then, after a 100+ hours... lament that it's over.
Which brings us to those who are returning to this title:
You know as well as I that this game has near to no replay value. Everything Oblivion has to offer can be experienced in a single playthrough, and the narrative has little to no variation (nor any substantial dialogue or narrative choices for those hopping for more RP in their RPG like the CRPGs that predated it).
It can be a hell of a ride, but with a story you can only fully revel in once, as a fresh player.
Otherwise you're only left to recall the insatiable desire to see and do everything until the memory of your previous experience is restored, which quickly dulls the experience.
However, on a personal note, I will add: that one thing I recalled was that this was one of the few games that truly made me feel as though I were fighting an endless army of demons; running, jumping, and cutting through one Oblivion gate after another...
And I felt it still, even years after its' initial release.
May it make you feel such heartiness as well.