Alenet's Oblivion Reloaded, shademe's MoreHeap, and Maskar's Maskar Oblivion Overhaul have breathed new life into the game stability aspects.
Kobal's OOO creatures and items addon added diversity that seamlessly blends in the game.
Nuska's Oblivion Character Overhaul v2 is a must to prevent potato-head issues.
Knights of the Nine Revelation is a big and polished lore-friendly quest mod that follows the official KoTN questline.
Better Cities and Unique Landscapes are going strong.
Hesu's mod collection is being localized from Japanese to English, with impressive results (I don't use this yet).
And most importantly, I may end up finishing the Oblivion main quest for the very first time this year!