This post is more about my opinions regarding the expansion than about the convention I guess.
I am interested in seeing how Tauren Paladins, Gnome Priests and Troll Druids will come about lore wise. Most of the other new class combos either exist in the game as NPCs or aren't all that far fetched. Dwarven Shaman for example, exist in the Wildhammer Clan and Blood Elf Warriors were stated as a balance decision instead of a lore issue. A blue stated earlier on the General Forums that the official lore name for the cowadins would be Sunwalker, which I assume will tie into their sun worship. I guess the gnomes were too busy focusing on the holy light instead of focusing on say, retaking their city.
The removal is this level of content in a game, particularly for an MMO strikes me as odd. I wonder if it is going to be even more odd for the folks who start playing post-Cataclysm. But that said, I think that the revamping of Azeroth is a fantastic idea and quite frankly, well overdue. The Eastern Kingdoms and Kalimdor have had more than their fair share of use over the past 5 years. At the moment, they feel out of date in terms of leveling flow and types of quests available. Consequently, I find it very hard returning to the old world to level my lowbies alts, even with the boost in experience.
The Burning Crusade introduced a smoother quest flow and more natural zone progression, eliminating the need to mob grind experience and to run across multiple continents and zones to quest. It also introduced a few new mechanics to increase the quest quality; The bombing runs for example. But as a whole, I felt that the story lines felt disconnected from the rest of the lore. I don't know if this was intentional or not, given that the Outlands well, is an alien planet. I just didn't feel as connected to the WoW story as I had originally in vanilla WoW.
Wrath on the Lich King on the other hand, was all about story progression. Using the new phasing mechanic and the intertwining of the lore into the quests in such an interactive and visual manner really pulled me into the expansion. So much so that I had actually leveled my hunter to 80 shortly after Keiya (anyone in guild knows that this is an incredible feat given my track with alts). It heralded the return and continuation of story lines from familiar faces that we've seen in the old world; NPC's whom we have invested quite a bit of time with like Tirion Fordring, Bolvar Fordragon, etc.
Wrath retained the Burning Crusade's smooth progression without feeling disconnected. The Lich King looms over you throughout your journey to level 80 and is introduced very early on in the expansion. Blizzard also did an exceptional job of rehashing key events from Warcraft III for the folks who either are not familiar with the strategy games or who might not have remembered what occurred. By contrast, Illidan, though mentioned quite often in quest text, did not feel like an active part of the Burning Crusade, at least to me. He just sort of popped into play when the Black Temple patch went live. I think that this point illustrates how important the doing things is in a gaming environment. I wonder how different the first expansion might have been if he was played out early in the game like Arthas?
I am really looking forward to seeing the new quest mechanics and the lore interactivity in the old world when Cataclysm hits. I am actually looking forward to rolling and leveling a low level alt again! According to the WoW panels, they are going to be able to phase areas even more. The terrain will change significantly as you progress in certain areas (the presentation had screenshots). The developers also mentioned that they are working out phasing kinks. We supposedly, might be able to share a phase with party members. You can probably already guess at some of the changes based off of old world gripes regarding certain areas (too large, too boring, too large and too boring, etc).
I am also cautiously optimistic about the new stat streamlining. Some stats are redundant: Spirit and MP5 for example, while some stats like Armor Penetration just never worked out. It is one of those stats that very few people understand and is either awesome for certain classes and otter crap for others. There's a pretty high level of redundancy on gear that makes it difficult for certain class and spec combinations to determine if an item is an upgrade without consulting an Excel spreadsheet. Several of the changes should make gear less ambiguous: No more spirit on mage gear, no more AP on leather (no more rogueadins lol).
Oh one more thing: Battlenet 2.0 will allow you to talk with friends across Blizzard games and across WoW servers/factions. I have IRL friends strewn across various servers, so I'm looking forward to being able to chat with them all in game without having to log over or poke Facebook/Gtalk.