First, the controls, especially from a Eastern MMO, are very accommodating to different play-styles Eastern / Asian MMO's typically employ only the click-to-move function, while leaving the WSAD crowd out in the cold. Aion, due to the 'westernization' of the Asian client, allows you to use both methods of controls as well as disable the click to move feature. This is very accommodating to people moving from western MMO's and not forcing them to change their 'tried and true' keybind setups. From looking at the controls page, virtually all actions bars, functions and features were keybindable. The only exception I found was the Camera-Pan function, which was innately bound to middle mouse. I'm hoping this is able to be rebound via patch or a registry-change, however I'm not super hopeful. Despite the camera functionality, the NCSoft team has done a great job at getting a Eastern MMO's control set to match that to which their American and European customers are accustomed to.
Looking over the controls and the basic User interface; the 'stock' package is actually quite adequate. Featuring standard MMO items (horizontal & vertical action bars, minimap, HP/MP/DP indicators). The quest log is a little lacking, as quest objectives aren't clearly defined nor a general direction given on where to find them; however a 'locate' function is in place to help you identify areas of interest; but this is quite buried in the UI itself. An indicator of combat or aggro isn't currently implemented; however, I understand that the UI is written in XML with a decent API, so hopefully we'll see the same degree of addons out for Aion as we have for WoW. As far as the client is concerned, the responsiveness is much better than Warhammer's, giving almost instantaneous response when an action or ability is activated. The only issue I ran into periodically is the Global Cool Down (GCD) acts a little 'funny' when casting. Because the GCD fires after the spell's cool down has started; it sometimes appears that there's a 2nd GCD in place. The games snappiness and fluidity extends beyond the hot-bars to the avatars themselves; with polished animations, fluid rag doll movements and realistic 'idle' effects, the animations far surpass anything that can be found in Warhammer. Combat animations are crisp and dramatic, which is a feature of Eastern MMO's and Anime. With Massive swords, dramatic flips and maneuvers, character's combat stances and actions may not be the most realistic, however they carry the same stylistic animations, motions and gestures that are common to Eastern media.
So far as mechanics go, we haven't seen enough of the math or formulas to determine how items are working behind the scenes, but with community greats such as Death & Taxes, Elitest Jerks and K&G trying Aion out, it shouldn't be long before we start to see the theorycrafting and numbers that make the game work. One thing 
is for sure though; we're seeing a comeback of our long lost love: the Random Number Generator. Having been absent throughout the development of Warhammer and Champions Online, the RNG is back and in full force; giving combat some randomness that will allow for a more dynamic play style. So far as tackling the customization issues, Aion is going to use Stigma(s) for character customization and Mana/Super/God stones for gear customization. If you're familiar with Warhammer's tactic system, then you'll feel right at home with Aion's stigma system, except that instead of ability enhancements, they're just entirely new abilities. Gear customization is going to be done similar to Warcrafts' Jewelcrafting, where each item has a set number of sockets, and stones fill the socket's voids, allowing you to further develop you characters gear and itemization.
The overall theme of Aion, coupled with the gameplay, feels much more like an older MMO than a new breed of the genre. With a slower leveling pace, only 50 levels and a death penalty, Aion is instating many of the items that MMO's have gotten rid of recently. Aion's leveling experience doesn't appear to be a quick treadmill, instead it appears to be a slow and steady uphill climb, much like DAoC 1.0 and Everquest. With a death penalty in place, it mirrors MMO's of old such as DAoC, EQ and AC; forgoing the 'easy' death penalty we observer in games today such as LotRO and WoW. While it has seemed to grab some of the best features of the older members of the western genre, one item it retains from it's eastern counterparts is it's reliance on money (Kinah) for *everything*. Eastern MMO's typically place a very heavy reliance on cash; and Aion is no exception. From flying to teleporting to simply binding at a new location, the games currency is the end all and be all of furthering your progression. The requirement of cash drives the economies of similar games such as Guild Wars, Lineage and Lineage II that can sometimes see exorbitant prices on desired items as well as increasing the number of bots and gold-sellers in your game. The last thematic item of note that it retains from it's eastern cohorts is it's reliance on grinding. Grinding, or the repeated killing of monsters that yield experience, isn't a new or even negative feature of MMO's, however recent trends in games have gotten away from 'grinding' and more towards a goal-oriented instanced dungeon / quest style of game play Western MMO players are notorious for their short attention spans and inability to repeatedly do menial tasks, while eastern players are know for their ability (and enjoyment) of grinding for levels on end. While there have been some successful Western MMO's that have relied on grinding as a major part of their leveling progression, Dark Age of Camelot being one of them, it will be and item to keep and eye on in the future.
This concludes my very brief portion over these features. There is so much depth to a "good" MMO (and I believe Aion will be a "good" MMO) that it's so hard to cover all of it's features in even a three part review; however take this as a brief explanation of the game from my point of view. The next portion of my review will feature what I think Aion is doing very well at, what I feel could be improved, what I'm leery of going into release and my overall feeling of the game.
Utilizing the Cry-Engine, NCSoft has issued forth another Competitive advantage... currently there is no other MMO that is as graphics detailed as Aion, save Age of Conan, however Aion does it without the major Graphics limitations and issues. Native AA is implemented in the engine currently, up to 8x AA, and Hardware Supported Bloom effects (via Cryengine) are available as well. From playing the Beta last night while keeping task manager open, the game looks solid from a back-end perspective... no Graphics leak like AoC, and no Memory or Page File leak like WAR. Reflective textures as well as high-detail textures (with sliders! Warhammer - take notes) are in already, and the game runs extremely smoothly for being so graphics intensive. Once more players are on the screen plus when it starts being used on non-SLi rigs is when we'll see whether or not Aion has a graphics bust or win.
