Oblivion

Masterpiece

This is one of a few games where my opinion of it is probably blinded by nostalgia. I think the quests and world are so interesting. The interactivity, the hostility of everyone you come across and the demon invasion create a great fantasy setting. This game has some of the best writing for its quests. There are also some great unintentional funny moments where the AI was a bit overambitious for the time.

There are also some Immersive Sim like elements with the interactivity in the world, branching quests and the dynamic ways NPCs interact with each other.

I don't think this needs any mods to update the experience to the modern day but I do think you need to be aware of the levelling system, read the 'The Levelling Problem' section on the wiki here Oblivion Levelling. If you aren't aware you can make your character very weak by levelling up. Another option is to adjust the difficulty slider down a few notches when enemies start to become spongy. Or there is a mod which avoids the main issues called All +5 Attribute Modifiers.