While most of the stuff you'll get here will probably be workable, it's important to remember that people often don't have a firm idea of what they actually want, and also that their good ideas aren't for "everyday" encounters.
I.e. Kazz's woods flanking example. Great idea, makes a lot of sense, but there's the big problem that Romo brought up. And if you don't need a party and can in fact solo 7 mobs at once, is it stressful or easy? Will it be relatively balanced for all classes? If it's stressful, it probably shouldn't happen too often. If it's easy, is it really worth doing, since after the 3rd time you run into anything in the woods it will no longer be novel and be just as grindy as running between single, non-aiding mobs?
The other important thing to do here is to work with the other "departments" and make sure that if relatively-complex-for-an-MMO AI is used that there is a decent learning curve going on. WoW takes a lot of (rightfully deserved) flak for this in a couple of areas: Roles that play entirely different in group settings than solo settings aren't taught to those classes through any gameplay mechanic other than blundering through a group dungeon and hoping you don't waste everyone else's time. In raid situations where non-standard AI is used (Faction Champions having a revised threat table where dispelling, CCing, and healing all cause vastly more threat than usual and there is a threat wipe every few seconds), even though virtually every class and role has tools to cope with this in their spellbook, most players haven't even had half this shit on their action bars because it is useless in every other encounter, etc..
I find this interesting from the point of view of adding in a very DotA like concept to MMOs. What I mean is, giving factions fighting NPCs that go and attack quest objectives on a regular basis but will lose without player intervention.
A Warror player can tank much better than the melee NPCs can and so can make an NPC raid successful by protecting the ranger and healer NPCs.
A Priest player can heal much more intelligently and strongly than the healer NPCs and so he can make an NPC raid successful by prioritizing heal targets better at clutch moments etc.
In this way we are training players to play their role in a party environment.
Parties of players can go after hard objectives that the single players and NPC forces are too weak/unintelligent to take on. Things that require a raid strategy, etc that NPC forces aren't programmed to adapt to, they just fight in a predictable manner like DotA creeps.
This would actually be a really cool idea.
Imagine a game where you start out as a sort of amateur mercenary, only instead of that just being a lame backstory to explain why you're a wandering dude with combat skills, you actually have to play the part by offering your services to the petty warring chieftains of the land. They have mob soldiers of their own, but a skilled healer/wizard/warrior/tactician is sought for the difference they'll bring.
The first battles are small and inglorious; raids, reprisal missions, or just general thuggery. You'll have a small group of your own mobs, in the 4-12 range. As your prestige rises, so does your pay grade and your influence in battle. Gradually, you'll seek larger and larger clients and make a difference in battle to larger groups who will supply you with more soldiers.
As you do so, you can gradually integrate play with other humans, first in groups of two or three, still aiding the smaller tribes or local clans, and then in larger groups, aiding bigger regional powers. At first there would be little PvP, but eventually the PvP ratio increases, until the highest levels of play where mighty kings have many heroic generals (i.e. human players) in their pay. In such cases, a player may even "settle down" and formally join a faction... though perhaps a crafy or risk-loving player could serve two masters at once. Or you could simply have a true medieval system where you have several lords, but they're all ranked and you have one real Leige lord who always takes precedence.
After a player joins a faction on a more permanent basis (starting around the mid-levels), you can indroduce all the "second life" MMO frills, like houses, trophy goods, or local prestige. Imagine walking down the street of a town you reside in and having mobs thanking you for saving them in specific battles. Or even having one of them buy you a drink in the local watering hole! I mean, you wanna give people a sense of accomplishment, that'll beat the everliving hell out of watching numbered stats go up.