For players that have reached level 85, there are 2 new Battlegrounds in Cataclysm. The Battle of Gilneas is a 10 on 10 contest where players fight over 3 control points. Much like Arathi Basin, your team accumulates resources by holding one or more of these points, and the first team to reach 2000 resources wins.
Twin Peaks is another 10 vs. 10 Battleground but it uses capture-the-flag objectives akin to Warsong Gulch. With a river running through the middle it's a nice change of scenery, and they've thoughtfully put in two graveyards per side to reduce the graveyard camping that Warsong sometimes devolves into.
While these are very good Battlegrounds, I'm not sure we really needed two more 20-player maps that use game mechanics so similar to earlier Battlegrounds. There's a lot of potential for mid-size Battlegrounds that remains unexplored. Perhaps more significant is the addition of rated Battlegrounds, which allow pre-formed groups to compete in seasonal tournaments, much like the Arena system.
Level 85 players also have the option to jump into Tol Barad, which is divided into a new Wintergrasp-like PvP zone and the Peninsula that is the main daily quest hub in the expansion. The PvP zone is an 80 vs. 80 match on a map with Baradin Hold at the center, surrounded by 3 control points which the attacking side must take to win. I haven't spent much time in Tol Barad yet, but there are clearly balance issues which need to be addressed. This is largely because it's considerably more difficult for the attackers to capture and hold 3 buildings than it is for the defenders to hold one. It seems to me that win conditions more like Arathi Basin or Battle of Gilneas would be one remedy for this, as would requiring the points to be captured in a certain order. Rest assured that Blizzard has acknowledged the problem and is planning to fix it in a patch.
Guild Levels and Archaeology
The guild system has seen a major upgrade in version 4.0 of WoW. Guilds now earn experience and gain levels much like characters do. Rewards for guild advancement apply to everyone in the guild, and include things such as XP bonuses and reduced repair costs. We've seen similar features in other games, and they tend to strengthen the bond players have with their guild.
Archaeology is a new secondary profession which everyone can train along with Cooking, First Aid, and Fishing. It involves visiting various dig sites scattered around Azeroth and Outland, then using the Survey ability you are given to find fragments which can be combined into artifacts. Common artifacts aren't worth much, but rare artifacts include more desirable items such as weapons, mounts, and pets. Although WoW's secondary professions have never been much more than a diversion, I don't know how many players will be up for the travel required by Archaeology.
The Bottom Line
With such an enormous and varied player base, Blizzard is faced with the impossible task of keeping everyone happy. I don't agree with every change they've made to the game, but it's hard to deny that the net result is a better game overall. Regardless of how you feel about the game's evolution, there's a lot to do in Cataclysm. The leveling experience is greatly improved for new players, and those at level 80 have several months worth of new PvE challenges to work through, depending on how efficient their guild is. PvP fans may not be quite as thrilled with the expansion. Although rated Battlegrounds are a nice addition, the two new BGs aren't all that inventive and Tol Barad will definitely need fine-tuning, if not a major revision. Minor grievances aside, Cataclysm is another truly outstanding entry in the MMORPG genre, and it's proof positive that World of Warcraft's reign isn't over yet.