While I do think Yahtzee hit the nail on the head with most of his points, I think he missed out on the game's biggest flaw; its 'leveling up' system.
The game gives absolutely no motivation to level up, as the world's NPCs infuriatingly level up with the protagonist... a serious flaw in an RPG.
In an RPG, it always feels good to go back and dominate those NPCs that had given you a tough time earlier in the game. In Oblivion, even at level 20, you will still have your ass handed to you by meager street bandits. Heck, you will have as much difficulty in killing a beggar, as you did at level 1.
In great CRPGs like Baludr's Gate II, you could often go back and kill those creatures that had been too powerful for you to handle at lower levels.
In fact, in an early chapter of BG2, you encounter two separate dragons, both of which are almost invulnerable to your attacks at that stage, and are better left ignored. However, the game returns to the same location in chapter six, allowing you another crack at them, and thus letting you enjoy character's growth.
Unfortunately, none of these experiences are possible in Oblivion, largely because of its pathetic XP mechanics.