The only disadvantages compared to the "remastered" version,
the lack of achievements.

In every other aspects this game has higher quality

Better than Skyrim, provided you're playing a character that uses magic. Alot of people think Oblivion's main issue is the obtuse leveling system that makes it difficult to get the maximum amount of attribute points per level, but that's an overstated issue since attributes suck and most of your damage and whatnot comes from skills. The real problem is that pure physical damage sucks, so if you're playing a pure warrior or rogue you simply don't do enough damage to keep up with the enemy scaling. If you accept these problems and just use magic, the game is fantastic. If you avoid magic altogether then you're going to have a bad time unless you turn the difficulty down.

You go through absolute hell getting the mods but then it's great