One example is that quest where you're supposed to kill three ogres coming at you in order to rescue a noble's daughter. One already is tough, but three?

Or the Oblivion gates at higher levels. You often will find yourself surrounded by three dremoras, or maybe one xivilai and two daedroth. Facing four of them isn't too uncommon either.

Or just generally any situation where there are too many strong enemies attacking you at the same time.

Sometimes. But most of the time, I feel the game is just a bit too easy on the player. And I think that's what makes the exceptions seem that much harder.

I've never found any situation in Oblivion that couldn't be handled at normal difficulty, by a reasonably well-developed character. Example, three ogres are no problem if you cast Command on one of them, and make him your friend.

Yep, I figure it's generally easier for mages.

But a melee character is gonna stand there trying to block the repeated blows all day.

The only time I find myself in situations like you describe is when I have leveled my character past their defense/attack/recovery skills. Stock Leveling in this game is kind of tricky. To the point that I only have two skills in my majors that I use all the time, the rest are support skills that are used sparingly, and have alternatives. This way as I level up, I am able to handle what the game throws at me.

If your on PC, the CM Partners mod can help with groups and gangs.

If you do the quest to purge the daedra from Kvatch at level 20, you're gonna have a baaad time.

Especially because the enemies tend to focus on you and ignore everyone else.

Not one of my melee characters. They know better than to try to use such a poor strategy.

I like a challenge, I wish there were more absurd enemies in TES. Like worthwhile bosses and loot in dungeons, instead of just a boring chest with nothing in it.

I find the combat mechanics for melee battles more difficult than anything. I go to swing and they're suddenly behind me. or, when fighting multiple enemies they are all stacked and it's just a swing-fest. the spacing and range of weapons, etc. is all off.

there's nothing wrong with multiple enemies swinging at me at the same time, but, the way it's done in oblivion is wrong and makes for poor melee fighting.

"Standing there" would be the problem. The solution with a melee character is to move around, make use of the terrain, and take advantage of your greater speed/agility. Ogres are slow and dumb, and they should be the ones "standing there."

You don't really need to get hit by all those blows.