It sure does look like 2006's Oblivion, but much prettier building on the visuals in 2011's Skyrim. You can see the full video below for yourself if you want to spend half a workday oohing and aahing, but this is basically the world and quests in Oblivion as you remember them, just presented in the more refined Skyrim engine, with its improved graphics and less broken level progression.
But that first impression maybe undersells the work that's gone into Skyblivion. Features like underwater combat - which was available in Oblivion but missing in Skyrim - have been implemented here. The devs have "decided to give some weapons a very cool overhaul." The Umbra Sword, for example, used to simply cast the Soul Trap spell on enemies it hit - now it can trap the soul of any creature that dies in your vicinity.
That's just the stuff from the first 15 minutes of the video, but there's plenty more new here, too. As our friends at PC Gamer note, the realm of the Daedric lord Peryite used to look like any other lava-filled hellscape in Oblivion - now it's been overhauled with a green, sickly tone fitting the Lord of Pestilence. Big story fights have also been enhanced. The battle against Mannimarco, the big boss of the Mage's Guild questline, takes place in a new area with new gameplay mechanics and a much greater level of challenge.
The devs also noted that the mod's already running on Steam Deck. So if you want some modernized Oblivion on the go, you're covered.