1. Full shadows: One of the most important elements of level design is lighting, and until this installment, their games dramatically lacked shadows. However, as you all know, Skyrim features a full set of dynamic lighting. This provides dark areas under and around structures, increases the contrast and enhances the areas the artists wish to draw the players attention too, resulting in a richer play experience.
2. Free leveling (No more classes ala Oblivion): They sort of did this in Fallout 3, but with Fallout's 'Level skills when you level' and generic experience system, it felt incomplete. However, in Skyrim, you play what skills feel right, and they level. Not only that, but focusing on skills increases the rate at which you level. This allows far more free and open playstyles, as opposed to Oblivion, where you were locked perminantly to a set of skills if you wanted to level.
3. Crafting/Enchanting/Alchemy: All of these things have been improved or added from previous titles. They saw how many mods added and altered these things, and they followed suit.
4. World detail: They are always improving on this, but in Skyrim they made some incredible steps in the right direction. They altered many of the lower level systems, and added things on large and small scales. They improved the manner in which large landforms like mountains were created, leaving the level designers plenty of opportunities to make incredible looking mountains and valleys, and they implemented much more minor things, like randomly generated insects that fly freely and while they lack actually AI, still make concious decisions based on their surroundings.
5. Realtime dialogue: People always complain about how menu's pause time, and I agree for the most part. I hated how dialogue in previous games froze time, often leaving the backdrop as you're told about something as a set of people, frozen in space. They hang there akwardly until the NPC is done talking and you resume normal gamemode. They took a huge step in Skyrim and talking no longer freezes the time. That alone greatly increases immersion and overall gameplay experience.
6. Scenes and dialogue views: This is more of a backbone/modding thing, but they finally added a system for complex scenes. In previous titles, scenes were scripted on a package-by-package basis, which took hours of time and was incredibly complicated to keep track of. Now you simply drag your packages and dialogue into the appropriate slot in the scene window, and you're done setting up your scene in a fraction of the time. Miss a step? Just add in right in the middle with the click of a button! This certainly allowed designers far more freedom and ease when adding complex interactivity.
7. Dungeon/Area FX: Bethesda has added a plethora of new FX items that allow for a far richer experience. Snow and leaves fluttering past the camera, many new sets of fogs and other items. This allows level designers to create the wonderous views like the large open caverns that leave you in awe! This also includes waterfalls and creeks, which make the world feel far more alive, and add that microdetail that you can enjoy as you take a stroll in the woods.
8. Animation: Bethesda implemented a whole new animation system this time around, and it's done wonders! Everything is far more lifelike and less stiff that previous titles. This also allowed them to do the melee kill animations which are bounds better than you basic Fallout 3 bat VATS kill!
9. Dual Wielding: Is it perfect? No. But is it at least there? Yes! I've wanted to dual wield for ages and they've finally given me the ability to do so. Sword and sword, axe and spell, shield and spell. A wide variety of gameplay styles is opened up by the addition of basic dual wielding.
10. Radiant Quests: They aren't major, and some people argue unimportant or poorly written, but Radiant Story is their way of breaking randomized gameplay into the engine. Bounties to kill bandits, other stories that are different every time. I enjoy this not so much for what it adds to Skyrim, but what it means for their future games. They attempted this in Oblivion and failed. But it made it into Skyrim, and that's a huge step for them in the direction of randomized, dynamic content.
I think this is their best game yet, and they are just getting better and better. They have my upmost respect as developers, and I think they do amazing things. Better yet, their games are truely unique. No other company in the world makes games of this size that are persistant, and this detailed.
I hope you never stop making amazing games Bethesda.
Alexander J. Velicky