I'm playing with OOO, but I'm sure even in vanilla oblivion you'll encounter this:
I was wandering somewhere and found a fort. I enter, then I find a room with 4 marauders plus a warlord. How will you even survive that assault?
If you'r a warrior, sure you can tank, but a 5 marauder attack will be hard, with them holding warhammers and axes.
If your a mage not adept at casting illusion spells, you're in even bigger trouble, unless you can one shot everything.
If your a thief, then you'r going to have a hard time at them not detecting you while poisons do the work.
For one, I don't go rushing in, announcing my arrival to all the marauders. That being said, I play mostly as a thief/ assassin backed up by magic. Marauders are usually some of the easiest foes to stay hidden from and snipe away at them. Just stay behind them/ keep them facing away from you. If you can't stay very well hidden from them (they keep seeing you) then either your sneak skill isn't high enough yet or your thieving/ assassin skills need some work.

For a pure warrior type, other than using restorative potions/ magic, all I can think of is back yourself into a narrow corner/ corridor so you only have to deal with them one at a time. That way the nearest one attacking you will keep the others out of reach just by being between you and the rest.
Do a power move to paralyze or knock down one of them and focus on the ones still standing until the knocked down foe gets back up.
Eliminate the weakest ones first to bring down the numbers faster, allowing you to dodge and make more time to strategize with fewer numbers of opponents.
If there are any archers in the mix, try to get the near foes into a crossfire of the arrows (keep nearest melee foe between you and the archer foe).
I don't think it unfair to drink some restore fatigue potions, to keep your attack power at max. Melee can consume considerable fatigue.
Of course, enchanted equipment (including weapons) can help a lot.