I am most excited by the changes to the raiding scene; where 10 man raids become a possible alternative to 25 man raiding, I feel 10 man raiding offers more challenge and allows a tighter-nit group of people to interact within the WoW raid scene without potentially feeling that the difficulty is scaled down significantly. This presents huge opportunities for hard-core guilds that only want to raid for a limited schedule guilds in the 25 man scene like Minions Of Mithril have already performed into the top 200 and top 100 raid scene on live using dedication and a good player base. With the smaller raid size and hopefully challenging content this would provide the ideal platform for a group of friends to play at the level they desire without devoting their souls too the gaming overlords. This to me seems a great opportunity to be both more competative and spend less time raiding. Tight-nit players would be able to perform much better then 25 players with less knowledge of each other and although 25 man guilds can be highly-interactive, there are clicks and groups that form regardless; this is especially evident in European guilds where national language barriers seperate groups of players more often then not. I have had the pleasure of playing with alot of remarkable European players from many countries and this is great but I feel it's less of a choice for them and more of a necessity to get the content they desire. I am not saying this is a bad aspect alot of these players became friends and I expect this will still happen. However one can potentially get a guild with more like-minded players with a smaller raid size.
10 man raids have been really engadging since Karazhan and even UBRS (by the time I was playing it was 10 man effectively) was one of the most exciting dungeons when one attempted Lord Valathak. I always felt there to be some need for more 10 man raids that were seperate from the current content, yes I don't really like the smaller version of the same dungeon pattern but if the difficulty works out to be challenging enough i'd enjoy it. In the recent past 10 mans have had elements that were tuned far too high for a 10 man only guild and these guilds were few and far between, alot of low population realms could have more success with 10 man focussed guilds. I remember instances where it was only down to 3-4 players in a 25 man to cause wipes in 25 man instances, this was rather annoying and lead to many guilds disbanding. With the change to not allowing both 10 and 25 man resets this does kind of eliminate my complaint that repetition of content is boring (ToC instances are a great example of repetition is boring).
Now while I don't currently play WoW I spent 4 years playing it, however I had said at the beginning of Wrath that I would stop playing once i'd seen ICC, I did after doing all the hardmodes apart form the lich king. I had lost interest in the game because the amount of thinking needed to perform well was so dumbed down, 10 mans were exciting but frustrating because they were always done on spare time, with alts/friends and on days when I had real life activities scheduled, I was missing out on the part of raiding that engadged me the most and when doing it, it was always harder then necessary due to people playing alt characters.
In Cataclysm I see a new game effectively where-by everything from the world design, quest content, raid content and leveling content is re-introduced in a new (learnt from experience) format that I really want to dive right into and taste, While my favourite change the raiding change won't be available in beta for a while(or potentially at all) I have good expectations for both the new leveling mechanics aswell as the revamps to the paladin class (which so far seem along the right track I was devistated when the wrath changes made retribution a faceroll class, where I had worked hard in sunwell to become decent for my gear 2k DPS on brutallus without my ideal gear, suddenly every paladin and their mother was doing 3k with any button push, even players who had unbound utiliity skills like Hand of Protection were equivalent to me and I lost ALOT of interest in the game. I am also quite excited for the healing changes because in wrath it became a spam feast.
In my mind the quallity of game design input has gone considerably up since wrath of the lich king, yes some features were scrapped due to time constraints but the general feel is that they want to bring new life to an aging game with aging systems. I will be playing Cataclysm regardless of getting a beta key just for the sake of experiencing the new leveling experience and probably will raid 10 mans and see how things go.
The current downsides with Cataclysm I see so far are some players may feel boxed in by the talent redesign (however I quite like it due to eradicating the need for expanding the talent system further), the potential lack of content to clear as people are used to this pattern of having an alt-main due to the avaiabillity of gear in 10 mans and 25 mans and my personal biggest fear; that the game won't be challenging enough(for players with any common sense most of wrath was a cake-walk, Ulduar was however beautiful in almost every way(it had flaws but they weren't terrible). Likewise ToC was a complete joke and the gating system used then made the progression slow and pain staking. I hope Cataclysm brings us to the point where hardmodes are for good players and normal modes are for the more casual gamer (which is fine) with the changes being that atleast classes will require some form of attention to perform well in raids be it through resource management or correct skill useage.
The things that stopped me playing were: The long wait till Cataclysm, the monotony of healing and paladin gameplay(im sure this is true for alot of classes), the time commitment(as a university student my alt gained very little attention and with GS I got in very few raids), GearScore as people have forgot how to value players on word of mouth and simple inspection and the current raid content once beat was a cake-walk(apart from lich king which I did not attempt to beat in heroic mode, however as someone who killed Muru pre 3.0 I expect I would have been able to kill him!!!).
What got me into WoW originally was the dungeon and raid game; and if done right it will keep me playing. That moment when you first enter an instance (for me it was the epic deadmines) was the moment I was fascinated by the gameplay dynamics that could evolve from this style of delivering content. For me it has never been about the loot but the experience of beating a challenging boss, like muru(or any of the sunwell bosses) or Nefarion. Sure I play the loot game but only because I want to get the most out of my character. Cataclysm brings a potential rejuvenation to the World of Warcraft world which I think could be what is needed to get players back and interested in the game, with even small changes to the old world the leveling experience is made somewhat fresh and exciting. I long to see the content changes, to work out the best possible rotations, to play alongside people in instances and to enjoy the exploration of the world of warcraft.