Except for unmodded Oblivion. It's just the opposite.

Arena is the hardest TES game. It gives you so many restrictions... Specially for me since I prefer Heavy Armor + Magic.. Can't do that in Arena.

Daggerfall.

Only because of the randomness of the creatures you can run into.
If there were chances you could run into a lvl 50 draugr death lord on your first mission in Skyrim then I might give it to Skyrim. Same for oblivion.

Dunno how you can claim a game as the hardest when it strives to only make you fight things level appropriate.

Running into the hardest mobs in game in your first 2 hours of Daggerfall made it the hardest.
If your just talking about controls wise... they are all easy:)

Skyrim. Ancient Dragons, nuff said.

It could be any of them. It depends how you play. Your character build will have far more impact on the difficulty of the game than any standard set by the devs. You can easily overpower a character by exploiting the character build and levelling mechanics whilst, conversely, you can just as easily gimp your character by picking awkward or underpowered attributes and abilities.

I'd say since Morrowind and Daggerfall provide you with more options and more abilities they are the games that could present the greatest challenge. Try playing a master linguist in Daggerfall and see how easy that is.

I would agree that Daggerfall and Morrowind were the hardest. Daggerfall in the sense that back then, you had to figure everything out on your own. Very little online help was available. The random dungeons were killer since the in game map was hopeless. This in its own made Daggerfall challenging.

Morrowind had challenging combat. Depending on your character some fights could be near to impossible without alot of pre planning. I always played a stealth character though so for me times were rough.

Um, what? Daggerfall has the best map utility of any TES game ever. Bar none.

Then my memory must have failed me. I recall having issues determining upper and lower levels in a dungeon map. Levels appeared as overlapping and were difficult to differentiate. Rotating didn't seem to help at all and ended up increasing the frustration.

Your memory hasn't failed you. The UESP even mentions this: "As one explores the larger dungeons the detailed map may become increasingly confusing."

But that would be true no matter what map system you use.

Anyway, while I admit that Daggerfall's map can be a little unwieldy sometimes, I've found it much more useful than the map systems of the other games, which can't even differentiate between multiple floor levels.

Any TES game that had me download an external program just to run was too hard.

I agree with SheridanR. Daggerfall had an excellent map, far better than any other TES. To me it seems that the people speaking against it are experiencing a PICNIC problem (person in chair, not in computer).

Daggerfall, due to its dungeons and glitches. I had to constantly save while in a dungeon lest I get lost or encounter a glitch.