well, did some research earlier today.
Let's put it this way. Plate tanks: Stances will be important now, more than ever before. Offensive stances: taunts become detaunts. Defensive stances: Taunts increase in power. avoidance tanks (brawlers): same for your primary offensive and defensive stances, however, the "combo" stance (combination of offensive and defensive) provides no bonus or penalty to your taunts.
There is now a new bar above the mobs. You still have the Health bar, and the power bar right below that, but now, right below the power bar is an "aggro" bar that can help you track how much aggro you have. Now, granted, I did this on my plate tanks (my main and main alt, both copied from the live server a while back), and I was forced to do this solo, but when in the defensive stance, the bar was present because I was constantly building aggro. when I was in the offensive stance, the bar disappeared quickly because I constantly "de-taunting".
This, combined with the actual hate/threat messages, will, I'm quite sure, add one more thing for the parsers to go ga-ga over and try to prove who is better and who is not. However, this is also a good thing and can help groups form up that can now get away from "we have a tank, we don't need any other fighters" mindset, since other fighters will be able to go offensive and not have to worry about grabbing aggro from the MT, or switch to defensive (or just shut off the stances) to grab adds if the off-tank.
ok, now to get to the second major changes to the fighter classes. I, honestly, don't know how they are judging how to set up the quality of the spells that remain (go off that base ability/spell, or take the highest quality from all the abilities/spells combined into that one), but it does clear up alot of hotbar space, and reduces the amount of time to rebuff. This does have some added benefit for classes like the guardian which has alot of "ally buffs" and temporary buffs which require hot bar slots, so any free slots available are always a good thing.
Do I think that all these changes are a good thing? I really can't say right now since getting a group on the test server is nigh-on impossible. From what I have seen, though, alot of thought was put into these changes, in an attempt to make sure that nothing was out of whack, over-powered, or weakened too much. I do have some screenshots of the "hate/threat" messages when I was on my guardian (one in offensive stance, one in defensive stance), so if anyone is interested in seeing something like that, just let me know and I will see what I can do.
ok, there's my 2cp, based on what I have seen on the test server. take it or leave it, that's your choice now.