These are known facts and rumors, bits marked with a * is a rumor and i have NOT confirmed.
There ARE going to be spoilers here, so be careful with what you read.
Please feel free to add what ever you have read hear or wish.

Setting ~

-
The game takes place primarily in Skyrim which is in the north of
Tamriel, it is not known if we will be able to go to other regions.
- Skyrim contains more than just snow, as seen in screenshots, there are rivers, lakes, waterfalls, forests, etc.
- The game is set 200 years after the events of Oblivion.
- *spoiler* Skyrim is in a state of civil war, which has just erupted in the beginning of the game.
- There are going to be five 'massive' cities in the game world.
- Dungeons are said to be a lot more unique in Skyrim, should be less repetetive.

Attributes and Leveling ~

- 18 Skills in total, this is 3 fewer than Oblivion and 11 fewer than Morrowind.
- New skill 'Enchantment'
- *New skill 'Smithing'
- There is no level cap, however after reaching level 50, it will take a lot longer to gain experience.
- At each level, you get a health upgrade and you can then select if you want to upgrade your Stamina or your Magicka.
-
You select perks when you level, just like in Fallout 3/New Vegas,
however it is not known how frequent these perks will be able to be
selected, or how many there will be.
- *Acrobatics and Athletics has been merged together, so has Mercantile and Speechcraft.

Creatures and NPCs ~

-
Known returning creatures are skeletons (however, some believe they
aren't actually skeletons), zombies, wolves, horses and elk.
- Confirmed new creatures are trolls, giant spiders, mountain and frost giants, dragons, mammoths and sabretoothed tigers.
- NPC face and body models have been significantly approved.
- NPCs are now more dynamic, and will interact with you more.

Combat ~

- Confirmed weapons are maces, axes, long swords, daggers, bow & arrow.
- There are 85 spells in the game.
- The 'Mysticysm' school of magic has been removed, it's spells have been dispersed to other schools.
- You can perform finishing moves which are unique to the weapon you are using and the creature you are fighting.
- You can dual wield weapons with many different combinations, including left hand spell, right hand weapon.
- You can fight using the shield, however it isn't known to which degree.
- Bethesda has put a lot of time into making the weapons feel real.
- Bow & Arrow is said to 'dominate' the long-distance combat, and are now slower to use, but more powerful.
-
They've tried to kill off 'cheap' combat tactics such as backpedaling,
when walking backwards you're not fast enough to keep your distance
from your opponent and at the same time attack him.

Story & Characters ~

- *spoiler* the player character is
believed to be the last remaining Dragonborn, a dragon hunter. The
Dragonborn were blessed by the Gods to be able to fight dragons on
equal terms.
- *spoiler* the player character has a mentor, a Nord
member of the Blades, he is voiced by Max Von Sydow who also narrated
the teaser trailer.
- *spoiler* it is believed that the Godlike
dragon Alduin, also known as the World-Eater is coming to Skyrim to
destroy the world.

General ~

- You can now sprint, at the cost of fatigue.
- You can now edit body features.
- Bethesda has hired a lot more voice actors this time to keep the dialogue fresh.
- Each race is going to look more distinct.
- Faces are now more emotive and are more distinguishable.
- There are now more activities to do in the cities, for example smithing, woodcutting and even cooking.
- When engaging in conversation, you no longer zoom in on the character you talk to, nor does it freeze time.

-
The NPC's are much more dynamic, for example, if you drop a weapon
inside a city, a young boy may pick it up, run after you, and ask if
you dropped it.
Another example of the same event is two men find the weapon and then fight over who gets to keep it.

-
The Oblivion styled enemy leveling & loot leveling is out, the one
in Skyrim is more in the style of Fallout 3, which in turn is more in
the style of Morrowind.
- Fast Travel is still in the game.
- 3rd person view has been improved.

- The new Radiant Story feature will tailor the sidequests found in the world to your playing style.
For
example, if you've gone around killing a lot of vampires, a woman may
approach you in a town, asking you to clear out a cave of Vampires.
The
game will then look at your playing history, see which caves you have
entired, then select a cave you haven't visited for the quest.The new
Radiant Story feature will tailor the sidequests found in the world to
your playing style.

- There are kids in the game.
- You can choose to play without the HUD.
-With
the new engine, water looks better, trees look better and snow falls
dynamically rather than just being a texture on the ground.
- Draw distance greatly increased.
- *Facial hair is now available for customization.

-There is a group of old men named the "Greybeards." They live at the
top of a mountain called the "Throat of the World," and are "highly
versed in the power of the dragons."
--Your character comes to them at some point in the game to be trained.

-Customizeable menu allows on-the-fly weapon/spell/item usage.

--Dragons will be farily common enemies.
---They
will attack towns at their whim. You may also encounter them out in the
wilderness. You will be forced to fight them back, (one on one of
course) or flee to safety.

--Instead of one large menu, you now open different smaller menus using the D-Pad
Credit goes to rivve and Curley

http://www.gamefaqs.com/boards/615803-the-elder-scrolls-v-skyrim/57744387?page=1

In b4 somebody makes a gourd joke.

My first thought was "Oh look! Another idiot misspelled "Guard"." My bad.

And thanks for this, nice to have it all in one place


Ladies and gents the man above me is a ninja

when you level up you get a point to put towards any perk you want you can save up those points to use later if you want

oh wait, wait, wait, there a minute.
I'm not any idiot.
I'm THE idiot who posted the original Confirmed Gourd Post
it really didn't last long but well there goes my 15 minutes of fame.

Uh. There's a skyrim information thread that has all of this in it plus a million other things. Sorry you did all that work for nothing :/

One day two gourds, who were best friends, were walking together down the street.
They stepped off the curb and a speeding car came around the corner and ran one of them over.
The uninjured gourd called 911 and helped his injured friend as best he was able.
The injured gourd was taken to emergency at the hospital and rushed into surgery.
After a long and agonizing wait, the doctor finally appeared.
He told the uninjured gourd, "I have good news, and I have bad news.

The good news is that your friend is going to pull through.

The bad news is that he's going to be a vegetable for the rest of his life.

There were no elk in Oblivion. There were deer. Not sure if there are multiple types of giants in the video it just says "giant".

Other confirmed animals: Cows, Hawks, Salmon, dogs, wolves, alpha wolves, fox, rabbit, mudcrab and bears. You can harvest beaks and feathers from the hawks.