After taking a long break from Oblivion, and after forgetting most of the game, I started playing it again and I'm really enjoying it.
Quests are a lot more fun and imaginative than I remembered, and they often give you enough information to do them without quest markers. NPCs and especially their schedules are suprisingly interesting. I like the chat system, there's a huge amount of topics for NPCs to talk about, and it takes a long time to get repetitive. There's also a lot of variety in magic, a bit more variety in weapons with shortswords, and you get to wear 5 pieces of armor! And the game has attributes and classes, which I prefer.
And with Oscuro's Oblivion Overhaul, there's little to no level scaling, so I don't have to sweat about getting those multipliers (although I never did before). I can face challenges at my own pace, and I can find valuable items that are worth it. In short, the world doesn't revolve around the number of my level anymore, and I'm free of it's shackles.
OOO also adds hand-placed loot, new items and artifacts, and with them the dungeons are actually quite fun. The overhaul adds much more, and I could honestly settle for a lot less. But I'm not complaining. Add in Unique Landscapes for unique landscapes, and that's pretty much it for me. The rest of the mods are purely visual: OCO, couple of animation mods and an ENB.
So yeah, the game has a lot of potential. It has great quests, which is really important, because it's the one aspect of the game that can't really be improved with mods. I can see why some think it's the best game of the three when modded.