LeFay was a response to an earlier post.
The basic skeleton of the plots are the same. Kill the big-bad guy. It's more the flesh built around it. To explain more in depth...
Mankar Camaron felt there, just to be there. He felt like he was just kind of the big bad guy, just because he fit the bill. However, in Morrowind you knew why Dagoth Ur was the big bad guy. He wasn't just a nobody, he was your best friend many years ago. He fought with you and against you.
It was also much less black-and-white. In Oblivion, when you went into the realms of oblivion (I'd say the Deadlands, but you also went into Peryite and Boethia's realms), they were basically 'Hell'. What was pouring out of He--the Deadlands? Dremora and Daedra (Demons) in armor that looks like it should raise your infamy as long as you wear it. Now, once we get past that we discover more. Who's behind this? Mehrunes Dagon, the Daedric Prince of Change and Natural Disasters. But in this, he was made to look like the epitome of evil. He wanted to CHANGE Tamriel.
In Morrowind, Lord Voryn Dagoth had gone mad over his many years of lifetime. There was a lot of lore about your relationship with him and the Tribunal in the game. While in Oblivion, you're simply just a nobody who was in the wrong cell at the right time. You had a purpose for this other than saving the world, you needed to right a wrong you made many years ago. By killing Dagoth, you righted it it took away the powers of the Tribunal, avenging yourself
Let's look at the factions...
The Fighters' Guild - They were obviously a knightly order of Daggerfall that had converted to a Fighters' Guild. They destroyed the enemy faction, because they were stealing jobs (less white), but mainly because they were so brutal (blinded). It portrayed Blackwood Company to be a bunch of blood-thirsty savages, even near the end.
The Mages' Guild - It made the necromancers appear to be crazed cultists. Now, I could understand the 'War of Necromancy' between the Mages' Guild and the Order of the Black Worm (IIRC), because there was backing to it on both sides (Travern made a stupid mistake and Mannimarco had a beef with the Mages' Guild and with all the out-of-work necromancers, he had a grand opportunity). However, implementation of Mannimarco and Black Soul Gems was poor. Mannimarco wasn't a brutal fiend that he was portrayed to be. The King of Worms wouldn't of made it known, period. And Black Soul Gems just tacked onto the 'good vs. evil'.
The Thieves' Guild - Robin Hood and his Merry Men (Renamed of course). I understand them somewhat looking out for the little guy, but it was rediculous. It made the Imperial Legion appear to be the bad guy (good vs. evil). I prefer the Daggerfall Thieves' Guild, or the Morrowind one personally. The Thieves' Guild was basically a faction of goody-two-shoes rebels who have a klepto problem.
The Dark Brotherhood - The professional, fear-inspiring assassins' guild had became an emo, puppy-kicking cultists of Tamriel faction. In Daggerfall, they felt like a guild of pros, in Oblivion they felt like the devs were trying too hard to make them be bad. In Morrowind, the Night Mother was a killable character (who wasn't a ghost) and Sithis was unheard of. In Oblivion, they had become a cultist society to a force of nature (one thing I've heard is basically worshipping gravity). I was fine with alot of them, until they preached Sithis and the orc in heavy armor. That was rediculous..."That'll be one six-year-old's party I'll never forget." The Dark Brotherhood would've killed him for such a gross misconduct (being caught).
We've discussed Oblivion's factions, lets take a look at the other side.
The Fighters' Guild lived up to what they should have been, an organization of mercenaries.
The Mages' Guild also did exactly what they were supposed to do, study.
The Thieves' Guild was a band of thieves, who had a lighter side (Bal Molagmar)
Now then...
The Morag Tong - An interesting approach to an assassins' guild. Lawful, skilled, honorable murderers who're highly trained in their craft and give loyalty to the local church. I found it more interesting than the cliche'd Dark Brotherhood.
The Imperial Cult - A religious faction which was dedicated to helping the poor and raising funds in the lower tiers. Once you got higher, you were dedicated to difficult duties like getting dangerous artifacts.
The Tribunal Temple - The local faith which had many darker elements to it. The gods they worshipped walked among them and they raised a lot of money for the poor. Many quests were about helping the less fortunate in the beginning, but as you rose in rank you began searching for artifacts that tended to be in Sixth House Bases, homes of the ancient enemy of the temple, Dagoth Ur (also known as Lord Voryn Dagoth, many years ago).
House Hlaalu - The most corrupt bunch of people Tamriel would ever see. In one quest, you can extort a governor of a village and then perform the task you promised him you wouldn't do. One thing that even makes it worse is the fact that he's also House Hlaalu! They appear to be the best House at the surface (welcoming Imperial faith and law), but as you delve deeper you discover it's merely means to an end.
Spoiler and they also are in strong relation with the local mafia
House Redoran - Your faithful knights in...bone armor? They help the poor and live by honor, and they strongly worship the Temple. However, that doesn't stop them from attacking the Imperialistic Hlaalu and the Xenophobic Telvanni. While they may protect the poor and uphold Temple values, they're a very aggressive bunch.
House Telvanni - The most powerful wizard on Nirn is in this house, Divayth Fyr . Many powerful wizards are from here; when you join you're little more than a disposable paper towel. However, as you rise in rank you start making a name for yourself in the House Telvanni and learn a lot of useful spells along the way. Eventually you even get a tower. But not any old tower, a mushroom tower!
Imperial Legion - The military of the empire (why it wasn't included in Oblivion is a question I'll be forced to ask myself forever). Your quests start out more as errands than tasks, but at the end you're recovering invaluable artifacts for the legion. There's more than a few options to take a 'dark' path on your quests.
Now let's take a glance at the expansions (mainly Tribunal and Knights of the Nine, but I'll touch on Bloodmoon and Shivering Isles)
In Tribunal, it really is an expansion. You continue regaining what was Lord Nerevar's, and now yours. It made sense for your actions in Mournhold.
In Knights of the Nine, if you were any of the following: Imperial, Redguard, Breton, Nord, Argonian, or Orc, it made sense. But if you were: Altmer, Dunmer, Bosmer, or Khajiit, it made little sense for you to be the Shezzarine. Why? Pelinial slaughtered mer (and khajiits, because he assumed they too were mer). This wasn't entirely the fault of the developers, but they should've done something that didn't involve a hero who massacred 4/10 of the playable races.
In Bloodmoon, you could become a werewolf and you had (most likely) already proven yourself to be a hero (as the Nerevarine). The Bloodhunt (IIRC) was beginning. You being the most suitable hero had to be the defender of Tamriel from Hircine. Naturally, you succeeded or else we'd have no Oblivion. You really had no choice in whether or not you wanted to do this.
In Shivering Isles, you could've been just some no-one explorer who wanted a sense of adventure. Okay, I understand that. However, in the Realm of the Madgod, it'd be very unlikely you'd be sane after a few days. It was also a little rediculous how easily you advanced to be the realm's (not Mania or Dementia's) Duke if you will (more of a viceroy, but...). There'd most likely be several people in front of you in the list, no matter how much you did. I honestly believe the Champion of Cyrodiil imagined all of the events that occured in the Shivering Isles.
Is it logical that someone who had only been there for about a week or two would be a Duke or Duchess of Mania or Dementia? No... However, it was possible.
Sorry, but I found that silly.
Also, level scaling is a topic that need not be discussed.