After about half a trillion attempts to play this game, including the aborted one I wrote about at the top of this page, it's finally clicked for me. Enjoying the core gameplay loop of just walking across the map and fucking people's shit up.
Minimal modlist with Ascension, Unique Landscapes, and UOP, one or two mods to reduce level-scaling, plus a couple other minor mostly-cosmetic tweaks.
The Bethesda-ness is strong though, because, no joke, about two minutes after I said out loud "fuck me, I'm actually enjoying this!" the game crashed to desktop for no reason, and then failed to load both my quicksave and autosave. Averted disaster by restoring the autosave backup and relying on manual saves from then on.
I still wish the game was something much, much, much more than it actually is, but that's true of every Elder Scrolls game, especially post-Daggerfall, so whatever. Oblivion's always been a sticking point for me, it's the one entry in the TES series that I just couldn't fully get into because it was too shit, but it seems to be working for me at long last. Looking forward to uncovering the whole map, meeting lots of potato-faced fools, and entering at least fifty identical caves.