Okay after a couple of weeks in GE being in the game I have more observations.
1. I've seen a lot of GE feedback about difficult some of the battle are. I myself get my butt routinely kicked in the last two encoutners of level 3 difficulty GE. I have a Progressive Era Town Hall, I have a +79%/+72% combat bonus, an Alcatraz, every PE unit type, PE Champions, and Rogues. And those last two encounters with 2-waves of 8 units each, all with a +65%/+65% combat bonus really kick me in the keyster. The thing is I love it! GE is supposed to be challenging. I am forced to spend a lot more time considering: unit type match-ups, terrain utilization, and even surrendering. (And I'm the type of player who usually never surrenders in a battle and instead forces himself to find a way to win, even in less than ideal circumstances.) So GE has forced me to really study all aspects of FoE combat more closely and even change my GB leveling priorities around to increase my combat bonus higher. And this is all a good thing. Because the risk factor must equal the reward factor (see 2 below.)
2. As to questions many have posed about the cost of unlocking higher GE difficulty levels compared to the value, I say the value is more than fair, provided your guild members are active enough and actually have cities that allow them to take advantage of GE. As others have pointed out even the most active GvG guilds can score about 2-3 days worth of guild power per week through GE, so the guild benefit is quite high. But let us not forget the person rewards on top of the guild benefits. I've scored at least 50 diamonds every week so far in GE on my main world, and I don't even finish level 3 difficulty. I've also scored a preimium decoration that my city really needed. I have lost count on how many unattached units (including Rogues) I have scored; but this number is huge. I have also seen potential prizes of: SoK, Bazaar, Reno Kit, Tiger's Den, premium buildings. So I find the personal rewards are quite extraordinary, and every player who comes to chat in my guild expressed excitement about participating in GE.
3. However, I can also see GE could possibly lead to the unintended consequence of active guilds, who really want to unlock level 2 and level 3 difficulty every week, dropping their less active (notice I did not say inactive here) guild members. I'm not talking about inactive players (shown red in guild member lists), I'm talking about players who are not red, but who just do not participate in GE. I'm one of my guild's founders on Noarsil, and I'm usually the guy who decides if we are going to unlock level 2 or level 3. Three things go into my decision making.
A. The resoundingly loud calls from our more active guild members to unlock the harder levels, and the goods donations to go with them.
B. The goods cost, top-to-bottom, in our guild versus the goods we need to maintain to support our active GvG campaign.
C. The number of 0s I see listed next to every guild member's name each week in the GE progress list.
Of the three decision criteria above, C. is going to force some guilds to make really tough choices on whether or not to keep players. I have already seen some guilds on my server dump a bunch of members. The goods cost for my guild to unlock both levels is somewhere around 5,500 total goods each week, and we have guild members from AFE down through EMA.
I know that Inno Games tends to try to preserve and encourage the social aspects of the game. (Thus have things like we can have 140 players on our friends list but we can only invite 80 ourselves, which means we must constantly solicit newer players to invites us.) I go back to my earlier feedback—letting guilds pay medals from treasury in place of missing goods to unlock levels would be a good idea, just use the same medals↔goods ratios as used in Recurring Quest rewards, so 5 Iron Age goods = 10 medals, 5 HMA goods = 30 medals, 5 Colonial Age goods = 70 medals, and so on. This would help encourage guilds retain less active members longer, by letting them pay medals in place of goods.
Otherwise, expect to see some guild purge a bunch of less active players in order to reduce their goods cost to unlock GE levels.